Fix missing return statement in VertexFormat validation.

BUG=angleproject:2063

Change-Id: Idc1c7b42ed0a2545d9ad4f3c645d0dea2c85c11e
Reviewed-on: https://chromium-review.googlesource.com/533273
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/validationES.cpp b/src/libANGLE/validationES.cpp
index 30044f5..97c8d85 100644
--- a/src/libANGLE/validationES.cpp
+++ b/src/libANGLE/validationES.cpp
@@ -4732,6 +4732,7 @@
     if (size < 1 || size > 4)
     {
         context->handleError(InvalidValue() << "size must be between one and four.");
+        return false;
     }
 
     switch (type)