Minor fix in Ganesh shader generation.

R=bsalomon@google.com

Author: skaslev@chromium.org

Review URL: https://codereview.chromium.org/78843006

git-svn-id: http://skia.googlecode.com/svn/trunk/src@12343 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gpu/gl/GrGLSL.cpp b/gpu/gl/GrGLSL.cpp
index 0f740d9..dce44f3 100644
--- a/gpu/gl/GrGLSL.cpp
+++ b/gpu/gl/GrGLSL.cpp
@@ -86,6 +86,7 @@
 
     if (mulFactor.isZeros()) {
         outAppend->appendf("%s = vec4(0);\n", vec4VarName);
+    } else {
+        outAppend->appendf("%s *= %s;\n", vec4VarName, mulFactor.c_str());
     }
-    outAppend->appendf("%s *= %s;\n", vec4VarName, mulFactor.c_str());
 }