Fix error reported by ASAN in 5782.asan.0.7113.pdf

==32161== ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6008000e3bcf at pc 0x7f66bae0e117 bp 0x7fffcb54ea70 sp 0x7fffcb54ea68
READ of size 1 at 0x6008000e3bcf thread T0
    #0 0x7f66bae0e116 in GooString::getChar(int) /home/tsdgeos/devel/poppler/goo/GooString.h:119
    #1 0x7f66bafb5dca in LinkURI::LinkURI(Object*, GooString*) /home/tsdgeos/devel/poppler/poppler/Link.cc:562
    #2 0x7f66bafb2a05 in LinkAction::parseAction(Object*, GooString*) /home/tsdgeos/devel/poppler/poppler/Link.cc:98
    #3 0x7f66bae69c0e in AnnotLink::initialize(PDFDoc*, Dict*) /home/tsdgeos/devel/poppler/poppler/Annot.cc:2621
    #4 0x7f66bae698d9 in AnnotLink::AnnotLink(PDFDoc*, Dict*, Object*) /home/tsdgeos/devel/poppler/poppler/Annot.cc:2596
    #5 0x7f66bae8d998 in Annots::createAnnot(Dict*, Object*) /home/tsdgeos/devel/poppler/poppler/Annot.cc:6737
    #6 0x7f66bae8d269 in Annots::Annots(PDFDoc*, int, Object*) /home/tsdgeos/devel/poppler/poppler/Annot.cc:6683
    #7 0x7f66bafc750d in Page::getAnnots(XRef*) /home/tsdgeos/devel/poppler/poppler/Page.cc:402
    #8 0x7f66bafc8e66 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:595
    #9 0x7f66bafd02fd 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
    #10 0x40311e in savePageSlice(PDFDoc*, SplashOutputDev*, int, int, int, int, int, double, double, char*) /home/tsdgeos/devel/poppler/utils/pdftoppm.cc:222
    #11 0x404416 in main /home/tsdgeos/devel/poppler/utils/pdftoppm.cc:521
    #12 0x7f66ba5f0ec4 (/lib/x86_64-linux-gnu/libc.so.6+0x21ec4)
    #13 0x401d58 in _start (/home/tsdgeos/devel/poppler/build-debug/utils/pdftoppm+0x401d58)

poppler/Link.cc

@@ -16,7 +16,7 @@
 // Copyright (C) 2006, 2008 Pino Toscano <[email protected]>
 // Copyright (C) 2007, 2010, 2011 Carlos Garcia Campos <[email protected]>
 // Copyright (C) 2008 Hugo Mercier <[email protected]>
-// Copyright (C) 2008-2010, 2012, 2013 Albert Astals Cid <[email protected]>
+// Copyright (C) 2008-2010, 2012-2014 Albert Astals Cid <[email protected]>
 // Copyright (C) 2009 Kovid Goyal <[email protected]>
 // Copyright (C) 2009 Ilya Gorenbein <[email protected]>
 // Copyright (C) 2012 Tobias Koening <[email protected]>
@@ -559,9 +559,11 @@ LinkURI::LinkURI(Object *uriObj, GooString *baseURI) {
       // relative URI
       if (baseURI) {
 	uri = baseURI->copy();
-	c = uri->getChar(uri->getLength() - 1);
-	if (c != '/' && c != '?') {
-	  uri->append('/');
+	if (uri->getLength() > 0) {
+	  c = uri->getChar(uri->getLength() - 1);
+	  if (c != '/' && c != '?') {
+	    uri->append('/');
+	  }
 	}
 	if (uri2->getChar(0) == '/') {
 	  uri->append(uri2->getCString() + 1, uri2->getLength() - 1);