Do not truncate the filter array in PDF_DataDecode().

It is not needed to fix https://crbug.com/552046 and it causes different
bug.

BUG=chromium:750993

Change-Id: I11627045bd3e73fb439884c3362ab1c26eb95fe3
Reviewed-on: https://pdfium-review.googlesource.com/9990
Reviewed-by: Oliver Chang <ochang@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>

core/fpdfapi/parser/fpdf_parser_decode.cpp

diff --git a/core/fpdfapi/parser/fpdf_parser_decode.cpp b/core/fpdfapi/parser/fpdf_parser_decode.cpp
index ddd6b14..77024f2 100644
--- a/core/fpdfapi/parser/fpdf_parser_decode.cpp
+++ b/core/fpdfapi/parser/fpdf_parser_decode.cpp
@@ -397,8 +397,6 @@
       *pImageParms = pParam;
       *dest_buf = last_buf;
       *dest_size = last_size;
-      if (CPDF_Array* pDecoders = pDecoder->AsArray())
-        pDecoders->Truncate(i + 1);
       return true;
     }
     if (last_buf != src_buf)