Bug 1338108 - The result of adding any percentage factor to a size that is zero should also be zero. r=dholbert

MozReview-Commit-ID: OzOCjvcz0A

layout/base/nsLayoutUtils.h

@@ -1450,13 +1450,14 @@ public:
   /**
    * This function increases an initial intrinsic size, 'aCurrent', according
    * to the given 'aPercent', such that the size-increase makes up exactly
-   * 'aPercent' percent of the returned value.  If 'aPercent' is less than
-   * or equal to zero the original 'aCurrent' value is returned. If 'aPercent'
-   * is greater than or equal to 1.0 the value nscoord_MAX is returned.
+   * 'aPercent' percent of the returned value.  If 'aPercent' or 'aCurrent' are
+   * less than or equal to zero the original 'aCurrent' value is returned.
+   * If 'aPercent' is greater than or equal to 1.0 the value nscoord_MAX is
+   * returned.
    */
   static nscoord AddPercents(nscoord aCurrent, float aPercent)
   {
-    if (aPercent > 0.0f) {
+    if (aPercent > 0.0f && aCurrent > 0) {
       return MOZ_UNLIKELY(aPercent >= 1.0f) ? nscoord_MAX
         : NSToCoordRound(float(aCurrent) / (1.0f - aPercent));
     }