Bug 1208023 - Avoid using a bad initial-scale when computing the CSS viewport. r=botond

--HG--
extra : commitid : bYtCKg4w35

dom/base/nsDocument.cpp

@@ -8050,7 +8050,7 @@ nsDocument::GetViewportInfo(const ScreenIntSize& aDisplaySize)
 
     // We need to perform a conversion, but only if the initial or maximum
     // scale were set explicitly by the user.
-    if (mValidScaleFloat) {
+    if (mValidScaleFloat && scaleFloat >= scaleMinFloat && scaleFloat <= scaleMaxFloat) {
       CSSSize displaySize = ScreenSize(aDisplaySize) / scaleFloat;
       size.width = std::max(size.width, displaySize.width);
       size.height = std::max(size.height, displaySize.height);