in the attempt to fix 627393, changed IFX_FileRead's readBlock to return the length it reads

core/fpdfapi/parser/fpdf_parser_utility.cpp

Index: core/fpdfapi/parser/fpdf_parser_utility.cpp
diff --git a/core/fpdfapi/parser/fpdf_parser_utility.cpp b/core/fpdfapi/parser/fpdf_parser_utility.cpp
index 630754a23b4ce3607486d5998fffba0a002f05b1..caee3355feaedeb03f63bd9ca42408cdc6054688 100644
--- a/core/fpdfapi/parser/fpdf_parser_utility.cpp
+++ b/core/fpdfapi/parser/fpdf_parser_utility.cpp
@@ -72,10 +72,10 @@ int32_t GetHeaderOffset(IFX_SeekableReadStream* pFile) {
   const size_t kBufSize = 4;
   uint8_t buf[kBufSize];
   for (int32_t offset = 0; offset <= 1024; ++offset) {
-    if (!pFile->ReadBlock(buf, offset, kBufSize))
+    if (pFile->ReadBlock(buf, offset, kBufSize) != kBufSize)
       return -1;
 
-    if (memcmp(buf, "%PDF", 4) == 0)
+    if (memcmp(buf, "%PDF", kBufSize) == 0)
       return offset;
   }
   return -1;