[buffer] function buffer_data_finish return NULL for empty buffer.

This behavior is required to match with same if begin of buffer required
to get in same condition.

[echo|exec|file_system] made casting meet with requirements from some
environments in order to meet align policy.

buffer.c

@@ -288,7 +288,8 @@ void* buffer_data_finish(const void* the_buffer_)
 	const struct buffer* the_buffer = (const struct buffer*)the_buffer_;
 
 	if (NULL == the_buffer ||
-		NULL == the_buffer->data)
+		NULL == the_buffer->data ||
+		the_buffer->size <= 0)
 	{
 		return NULL;
 	}

echo.c

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2019 - 2022 TheVice
+ * Copyright (c) 2019 - 2022, 2024 TheVice
  *
  */
 
@@ -181,9 +181,17 @@ uint8_t echo(
 			else
 			{
 #if defined(_WIN32)
-				result = (is_output_standard && REQUIRED_UNICODE_CONSOLE_AT_WINDOWS(encoding)) ?
-						 echo_win32(echo_get_win32_console_output(level), (const uint16_t*)message, (uint16_t)message_length) :
-						 (message_length == (ptrdiff_t)file_write(message, sizeof(uint8_t), message_length, file_stream));
+
+				if (is_output_standard && REQUIRED_UNICODE_CONSOLE_AT_WINDOWS(encoding))
+				{
+					result = echo_win32(echo_get_win32_console_output(level), (const uint16_t*)buffer_data(new_message, 0),
+										(uint16_t)message_length);
+				}
+				else
+				{
+					result = (message_length == (ptrdiff_t)file_write(message, sizeof(uint8_t), message_length, file_stream));
+				}
+
 #else
 				result = (message_length == (ptrdiff_t)file_write(message, sizeof(uint8_t), message_length, file_stream));
 #endif

exec.c

@@ -483,7 +483,7 @@ uint8_t exec(
 	}
 
 	const wchar_t* start = programW;
-	const wchar_t* finish = (const wchar_t*)(buffer_uint8_t_data(application, 0) + buffer_size(application));
+	const wchar_t* finish = (const wchar_t*)buffer_data_finish(application);
 	/**/
 	ptrdiff_t indices[3];
 	memset(indices, 0, sizeof(indices));

file_system.c

@@ -320,7 +320,7 @@ uint8_t directory_enumerate_file_system_entries_wchar_t(
 
 			if (file_system_get_id_of_file_entry() == entry_type)
 			{
-				finish = (const wchar_t*)(buffer_uint8_t_data(pattern, 0) + sizeof(wchar_t) * new_index);
+				finish = buffer_wchar_t_data(pattern, 0) + (sizeof(wchar_t) * new_index) / sizeof(wchar_t);
 
 				if (!buffer_resize(pattern, index * sizeof(wchar_t)) ||
 					!buffer_append_wchar_t(pattern, finish, delta))
@@ -334,7 +334,7 @@ uint8_t directory_enumerate_file_system_entries_wchar_t(
 		}
 		else if (file_system_get_id_of_directory_entry() == entry_type)
 		{
-			finish = (const wchar_t*)(buffer_uint8_t_data(pattern, 0) + sizeof(wchar_t) * new_index);
+			finish = buffer_wchar_t_data(pattern, 0) + (sizeof(wchar_t) * new_index) / sizeof(wchar_t);
 
 			if (!buffer_resize(pattern, index * sizeof(wchar_t)) ||
 				!buffer_append_wchar_t(pattern, finish, delta))
@@ -346,7 +346,7 @@ uint8_t directory_enumerate_file_system_entries_wchar_t(
 			continue;
 		}
 
-		finish = (const wchar_t*)(buffer_uint8_t_data(pattern, 0) + sizeof(wchar_t) * new_index);
+		finish = buffer_wchar_t_data(pattern, 0) + (sizeof(wchar_t) * new_index) / sizeof(wchar_t);
 
 		if (UTF8 == output_encoding)
 		{
@@ -597,7 +597,7 @@ uint8_t directory_create(const uint8_t* path)
 	wchar_t* path_start = buffer_wchar_t_data(pathW, 0);
 	/**/
 	const wchar_t* start = path_start;
-	const wchar_t* finish = (const wchar_t*)(buffer_uint8_t_data(pathW, 0) + buffer_size(pathW));
+	const wchar_t* finish = (const wchar_t*)buffer_data_finish(pathW);
 	/**/
 	file_system_set_position_after_pre_root_wchar_t(&start);
 
@@ -761,7 +761,7 @@ uint8_t directory_delete(const uint8_t* path)
 
 #if defined(_WIN32)
 		const wchar_t* start = buffer_wchar_t_data(entries, 0);
-		const wchar_t* finish = (const wchar_t*)(buffer_uint8_t_data(entries, 0) + buffer_size(entries));
+		const wchar_t* finish = (const wchar_t*)buffer_data_finish(entries);
 #else
 		const uint8_t* start = buffer_uint8_t_data(entries, 0);
 		const uint8_t* finish = start + buffer_size(entries);