Fix error reported by ASAN in 2279.asan.0.1904.pdf

==20507== ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60420000ff04 at pc 0x7fa1492e8012 bp 0x7fff8406d900 sp 0x7fff8406d8f8
READ of size 4 at 0x60420000ff04 thread T0
    #0 0x7fa1492e8011 in SplashFTFont::makeGlyph(int, int, int, SplashGlyphBitmap*, int, int, SplashClip*, SplashClipResult*) /home/tsdgeos/devel/poppler/splash/SplashFTFont.cc:284
    #1 0x7fa1492eda32 in SplashFont::getGlyph(int, int, int, SplashGlyphBitmap*, int, int, SplashClip*, SplashClipResult*) /home/tsdgeos/devel/poppler/splash/SplashFont.cc:168
    #2 0x7fa1492e7c69 in SplashFTFont::getGlyph(int, int, int, SplashGlyphBitmap*, int, int, SplashClip*, SplashClipResult*) /home/tsdgeos/devel/poppler/splash/SplashFTFont.cc:233
    #3 0x7fa1492b3368 in Splash::fillChar(double, double, int, SplashFont*) /home/tsdgeos/devel/poppler/splash/Splash.cc:2714
    #4 0x7fa149286a20 in SplashOutputDev::drawChar(GfxState*, double, double, double, double, double, double, unsigned int, int, unsigned int*, int) /home/tsdgeos/devel/poppler/poppler/SplashOutputDev.cc:2270
    #5 0x7fa1490e7599 in Gfx::doShowText(GooString*) /home/tsdgeos/devel/poppler/poppler/Gfx.cc:4054
    #6 0x7fa1490e4db0 in Gfx::opShowSpaceText(Object*, int) /home/tsdgeos/devel/poppler/poppler/Gfx.cc:3886
    #7 0x7fa1490c333a in Gfx::execOp(Object*, Object*, int) /home/tsdgeos/devel/poppler/poppler/Gfx.cc:903
    #8 0x7fa1490c250f in Gfx::go(bool) /home/tsdgeos/devel/poppler/poppler/Gfx.cc:762
    #9 0x7fa1490c2163 in Gfx::display(Object*, bool) /home/tsdgeos/devel/poppler/poppler/Gfx.cc:728
    #10 0x7fa1491a4dd1 in Page::displaySlice(OutputDev*, double, double, int, bool, bool, int, int, int, int, bool, bool (*)(void*), void*, bool (*)(Annot*, void*), void*, bool) /home/tsdgeos/devel/poppler/poppler/Page.cc:585
    #11 0x7fa1491ac2fd in PDFDoc::displayPageSlice(OutputDev*, int, double, double, int, bool, bool, bool, int, int, int, int, bool (*)(void*), void*, bool (*)(Annot*, void*), void*, bool) /home/tsdgeos/devel/poppler/poppler/PDFDoc.cc:503
    #12 0x40311e in savePageSlice(PDFDoc*, SplashOutputDev*, int, int, int, int, int, double, double, char*) /home/tsdgeos/devel/poppler/utils/pdftoppm.cc:222
    #13 0x404416 in main /home/tsdgeos/devel/poppler/utils/pdftoppm.cc:521
    #14 0x7fa1487ccec4 (/lib/x86_64-linux-gnu/libc.so.6+0x21ec4)
    #15 0x401d58 in _start (/home/tsdgeos/devel/poppler/build-debug/utils/pdftoppm+0x401d58)

splash/SplashFTFont.cc

@@ -11,7 +11,7 @@
 // All changes made under the Poppler project to this file are licensed
 // under GPL version 2 or later
 //
-// Copyright (C) 2005, 2007-2011 Albert Astals Cid <[email protected]>
+// Copyright (C) 2005, 2007-2011, 2014 Albert Astals Cid <[email protected]>
 // Copyright (C) 2006 Kristian Høgsberg <[email protected]>
 // Copyright (C) 2009 Petr Gajdos <[email protected]>
 // Copyright (C) 2010 Suzuki Toshiya <[email protected]>
@@ -280,7 +280,7 @@ GBool SplashFTFont::makeGlyph(int c, int xFrac, int yFrac,
   FT_Set_Transform(ff->face, &matrix, &offset);
   slot = ff->face->glyph;
 
-  if (ff->codeToGID && c < ff->codeToGIDLen) {
+  if (ff->codeToGID && c < ff->codeToGIDLen && c >= 0) {
     gid = (FT_UInt)ff->codeToGID[c];
   } else {
     gid = (FT_UInt)c;