Fix Visual Studio warning treated as error.

Was an implicit narrowing from size_t (64-bit) to unsigned int (32-bit).

Change-Id: I9726d70370d97da1bae2652bbce9db929179a292
Reviewed-on: https://swiftshader-review.googlesource.com/13469
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
diff --git a/src/OpenGL/libGLESv2/IndexDataManager.cpp b/src/OpenGL/libGLESv2/IndexDataManager.cpp
index 57d7f4b..a32b7d1 100644
--- a/src/OpenGL/libGLESv2/IndexDataManager.cpp
+++ b/src/OpenGL/libGLESv2/IndexDataManager.cpp
@@ -261,7 +261,7 @@
 		}
 		return vertexPerPrimitive;
 	case GL_POINTS:
-		*primitiveCount = count - restartIndices.size();
+		*primitiveCount = static_cast<unsigned int>(count - restartIndices.size());
 		return 1;
 	default:
 		UNREACHABLE(mode);