Elide empty variations

Don't add a "_" to the variant name if the variation name is empty.  For
example, when splitting a variant with name "foo" into variations "" and
"bar", the new variants would be named "foo" and "foo_bar" instead of
"foo_" and "foo_bar".

Change-Id: I82342d57e2a8e9f2d65a7d8d2872dcb7b3512899

context.go

@@ -1000,11 +1000,13 @@ func (c *Context) createVariations(origModule *moduleInfo, mutatorName string,
 		newModule.dependencyVariant = origModule.dependencyVariant.clone()
 		newModule.moduleProperties = newProperties
 
+		if variationName != "" {
 			if newModule.variantName == "" {
 				newModule.variantName = variationName
 			} else {
 				newModule.variantName += "_" + variationName
 			}
+		}
 
 		newModules = append(newModules, newModule)