Fix a regression for parsing '/' - commit a568ff2d  was too strict.

BUG=pdfium:326
R=dml@google.com

Review URL: https://codereview.chromium.org/1521543002 .

core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp

diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
index bc5d3ed..ca3a5f6 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
@@ -2125,10 +2125,6 @@
       if (key.IsEmpty())
         continue;
 
-      CFX_ByteStringC keyNoSlash(key.c_str() + 1, key.GetLength() - 1);
-      if (keyNoSlash.IsEmpty())
-        continue;
-
       if (key == FX_BSTRC("/Contents"))
         dwSignValuePos = m_Pos;
 
@@ -2136,6 +2132,7 @@
       if (!pObj)
         continue;
 
+      CFX_ByteStringC keyNoSlash(key.c_str() + 1, key.GetLength() - 1);
       // TODO(thestig): Remove this conditional once CPDF_Dictionary has a
       // better underlying map implementation.
       if (nKeys < 32) {