Fix CPDF_CIDFont::GlyphFromCharCode for fonts flagged with PDFFONT_SYMBOLIC

UnicodeFromCharCode should be tried even if the font is flagged as
PDFFONT_SYMBOLIC. The result should be checked in case it's empty. This
fixes some corpus tests that were being incorrectly rendered, as well as
the bug below.

A deps change will be required before landing this CL.

BUG=chromium:591303

Review-Url: https://codereview.chromium.org/2300893003
diff --git a/DEPS b/DEPS
index 37c9ac5..d17f7e0 100644
--- a/DEPS
+++ b/DEPS
@@ -14,7 +14,7 @@
   'gmock_revision': '29763965ab52f24565299976b936d1265cb6a271',
   'gtest_revision': '8245545b6dc9c4703e6496d1efd19e975ad2b038',
   'icu_revision': '2341038bf72869a5683a893a2b319a48ffec7f62',
-  'pdfium_tests_revision': '5867fa68fa3e00016d3e31374e84eb01a3db6ac7',
+  'pdfium_tests_revision': 'a7f9103f929c6ab5e2188c629d61797548e9c200',
   'skia_revision': '3ee255f259541eff1251c8007f9135e8d664346a',
   'tools_memory_revision': '427f10475e1a8d72424c29d00bf689122b738e5d',
   'trace_event_revision': '54b8455be9505c2cb0cf5c26bb86739c236471aa',
diff --git a/core/fpdfapi/fpdf_font/cpdf_cidfont.cpp b/core/fpdfapi/fpdf_font/cpdf_cidfont.cpp
index 2bd8867..df08781 100644
--- a/core/fpdfapi/fpdf_font/cpdf_cidfont.cpp
+++ b/core/fpdfapi/fpdf_font/cpdf_cidfont.cpp
@@ -631,8 +631,11 @@
         unicode = m_pCID2UnicodeMap->UnicodeFromCID(cid);
       if (unicode == 0)
         unicode = GetUnicodeFromCharCode(charcode);
-      if (unicode == 0 && !(m_Flags & PDFFONT_SYMBOLIC))
-        unicode = UnicodeFromCharCode(charcode).GetAt(0);
+      if (unicode == 0) {
+        CFX_WideString unicode_str = UnicodeFromCharCode(charcode);
+        if (!unicode_str.IsEmpty())
+          unicode = unicode_str.GetAt(0);
+      }
     }
     FXFT_Face face = m_Font.GetFace();
     if (unicode == 0) {