Detected memory leaks

[fouzhe]

I use Clang 6.0 and AddressSanitizer to build pdf2json v0.69, this file can cause memory leaks with the following command:

./pdf2json detected_memory_leaks.pdf 1.json

This is the ASAN information:

=================================================================
==15578==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 16 byte(s) in 1 object(s) allocated from:
    #0 0x516e58 in operator new(unsigned long) /home/fouzhe/llvm/llvm/projects/compiler-rt/lib/asan/asan_new_delete.cc:92
    #1 0x5e9bcf in GString::copy() /home/fouzhe/my_fuzz/pdf2json/xpdf/./../goo/GString.h:41:28
    #2 0x5e9bcf in GlobalParams::getTextEncodingName() /home/fouzhe/my_fuzz/pdf2json/xpdf/GlobalParams.cc:2256

Direct leak of 16 byte(s) in 1 object(s) allocated from:
    #0 0x516e58 in operator new(unsigned long) /home/fouzhe/llvm/llvm/projects/compiler-rt/lib/asan/asan_new_delete.cc:92
    #1 0x6094f1 in Page::getLinks(Catalog*) /home/fouzhe/my_fuzz/pdf2json/xpdf/Page.cc:254:11
    #2 0x60fe2e in PDFDoc::getLinks(int) /home/fouzhe/my_fuzz/pdf2json/xpdf/PDFDoc.cc:351:34
    #3 0x60fe2e in PDFDoc::displayPage(OutputDev*, int, double, double, int, int, int, int, int (*)(void*), void*) /home/fouzhe/my_fuzz/pdf2json/xpdf/PDFDoc.cc:320
    #4 0x60fe2e in PDFDoc::displayPages(OutputDev*, int, int, double, double, int, int, int, int, int (*)(void*), void*) /home/fouzhe/my_fuzz/pdf2json/xpdf/PDFDoc.cc:332

Indirect leak of 8 byte(s) in 1 object(s) allocated from:
    #0 0x517008 in operator new[](unsigned long) /home/fouzhe/llvm/llvm/projects/compiler-rt/lib/asan/asan_new_delete.cc:95
    #1 0x8cc5ce in GString::resize(int) /home/fouzhe/my_fuzz/pdf2json/goo/GString.cc:87:9
    #2 0x8cc5ce in GString::GString(GString*) /home/fouzhe/my_fuzz/pdf2json/goo/GString.cc:131

SUMMARY: AddressSanitizer: 40 byte(s) leaked in 3 allocation(s).