fix(MdSelect): infinite loop error, when no v-model provided (#2035)

Author: hastom

src/components/MdField/MdSelect/MdSelect.vue

@@ -283,9 +283,9 @@
         let isArray = Array.isArray(this.localValue)
 
         if (this.multiple && !isArray) {
-          this.localValue = this.setLocalValueIfMultiple()
+          this.setLocalValueIfMultiple()
         } else if (!this.multiple && isArray) {
-          this.localValue = this.setLocalValueIfNotMultiple()
+          this.setLocalValueIfNotMultiple()
         }
       },
       emitSelected (value) {