[truetype] Integer overflow issues.

Reported as

  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=7718

* src/truetype/ttinterp.c (Ins_MIRP): Use ADD_LONG.

ChangeLog

@@ -1,3 +1,13 @@
+2018-04-16  Werner Lemberg  <wl@gnu.org>
+
+	[truetype] Integer overflow issues.
+
+	Reported as
+
+	  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=7718
+
+	* src/truetype/ttinterp.c (Ins_MIRP): Use ADD_LONG.
+
 2018-04-15  Alexei Podtelezhnikov  <apodtele@gmail.com>
 
 	[build] Use `info' function of make 3.81.
@@ -46,7 +56,7 @@
 
 2018-04-10  Nikolaus Waxweiler  <madigens@gmail.com>
 
-	* CMakeLists.txt, builds/cmake/FindHarfBuzz.cmake: Extensive 
+	* CMakeLists.txt, builds/cmake/FindHarfBuzz.cmake: Extensive
 	modernization measures.
 
 	This brings up the minimum required CMake version to 2.8.12.
@@ -102,7 +112,7 @@
 	builds/windows/vc2008/freetype.vcproj,
 	builds/windows/visualce/freetype.vcproj,
 	builds/windows/visualce/freetype.dsp,
-	builds/windows/visualc/freetype.vcproj, 
+	builds/windows/visualc/freetype.vcproj,
 	builds/windows/visualc/freetype.dsp: Remove per-file compile flags.
 
 2018-04-04  Werner Lemberg  <wl@gnu.org>

src/truetype/ttinterp.c

@@ -6193,7 +6193,7 @@
     minimum_distance    = exc->GS.minimum_distance;
     control_value_cutin = exc->GS.control_value_cutin;
     point               = (FT_UShort)args[0];
-    cvtEntry            = (FT_ULong)( args[1] + 1 );
+    cvtEntry            = (FT_ULong)( ADD_LONG( args[1], 1 ) );
 
 #ifdef TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY
     if ( SUBPIXEL_HINTING_INFINALITY                        &&