Fix a leak in PDF_DataDecode() on failure.

Found using the test examples from https://crbug.com/537780

R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1376413003 .
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp
index 402a19e..2d6e9f3 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp
@@ -416,6 +416,7 @@
       FX_Free(last_buf);
     }
     if (offset == -1) {
+      FX_Free(new_buf);
       return FALSE;
     }
     last_buf = new_buf;