Make sure that iterator stays in bounds during IsHypen

BUG=chromium:782596,chromium:781804

Change-Id: I020be3cf813221bb8314f045d83014a25cb9a950
Reviewed-on: https://pdfium-review.googlesource.com/18070
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>

1 files changed, 5 insertions, 8 deletions

diff --git a/core/fpdftext/cpdf_textpage.cpp b/core/fpdftext/cpdf_textpage.cpp
index 6ccadff701..485fba24a8 100644
--- a/core/fpdftext/cpdf_textpage.cpp
+++ b/core/fpdftext/cpdf_textpage.cpp
@@ -1226,20 +1226,17 @@ bool CPDF_TextPage::IsHyphen(wchar_t curChar) const {
     return false;
 
   auto iter = curText.rbegin();
-  for (; iter != curText.rend() && *iter == 0x20; iter++) {
+  for (; (iter + 1) != curText.rend() && *iter == 0x20; iter++) {
     // Do nothing
   }
 
-  if (iter != curText.rend()) {
-    if (!IsHyphenCode(*iter))
-      return false;
+  if (!IsHyphenCode(*iter))
+    return false;
+
+  if ((iter + 1) != curText.rend()) {
     iter++;
     if (FXSYS_iswalpha(*iter) && FXSYS_iswalpha(*iter))
       return true;
-  } else {
-    iter--;
-    if (!IsHyphenCode(*iter))
-      return false;
   }
 
   const PAGECHAR_INFO* preInfo;