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

core/fpdfapi/edit/fpdf_edit_create.cpp

Index: core/fpdfapi/edit/fpdf_edit_create.cpp
diff --git a/core/fpdfapi/edit/fpdf_edit_create.cpp b/core/fpdfapi/edit/fpdf_edit_create.cpp
index a578a0a1141c81f80a64634c54c098b7ae428fed..1de9a577af22170ad457ec55e23358c577140768 100644
--- a/core/fpdfapi/edit/fpdf_edit_create.cpp
+++ b/core/fpdfapi/edit/fpdf_edit_create.cpp
@@ -1494,13 +1494,15 @@ int32_t CPDF_Creator::WriteDoc_Stage1(IFX_Pause* pPause) {
       uint32_t src_size = (uint32_t)(uintptr_t)m_Pos;
       while (src_size) {
         uint32_t block_size = src_size > 4096 ? 4096 : src_size;
-        if (!pSrcFile->ReadBlock(buffer, m_Offset - src_size, block_size)) {
+        uint32_t read_size =
+            pSrcFile->ReadBlock(buffer, m_Offset - src_size, block_size);
+        if (read_size != block_size && !pSrcFile->IsEOF()) {
           return -1;
         }
-        if (m_File.AppendBlock(buffer, block_size) < 0) {
+        if (m_File.AppendBlock(buffer, read_size) < 0) {
           return -1;
         }
-        src_size -= block_size;
+        src_size -= read_size;
         if (pPause && pPause->NeedToPauseNow()) {
           m_Pos = (void*)(uintptr_t)src_size;
           return 1;