fixed cancel button of background image prompt to not reset background image (fixes #13)

src/components/Menu.vue

@@ -1,16 +1,16 @@
 <template>
   <div id="controls">
     <Screenshot ref="screenshot"></Screenshot>
-    <span class="session">
-      <font-awesome-icon
-        @click="leaveSession"
-        icon="broadcast-tower"
-        v-if="session.sessionId"
+    <span
+      class="session"
       :class="{ spectator: session.isSpectator }"
+      v-if="session.sessionId"
+      @click="leaveSession"
       :title="
         `You're currently in a live game with ${session.playerCount} other players!`
       "
-      />
+    >
+      <font-awesome-icon icon="broadcast-tower" />
       {{ session.playerCount }}
     </span>
     <span class="camera">
@@ -127,10 +127,11 @@ export default {
       this.$refs.screenshot.capture(dimensions);
     },
     setBackground() {
-      this.$store.commit(
-        "setBackground",
-        prompt("Enter custom background URL")
-      );
+      const background = prompt("Enter custom background URL");
+      if (background || background === "") {
+        this.$store.commit("setBackground", background);
+      }
+
     },
     hostSession() {
       const sessionId = prompt(
@@ -248,21 +249,20 @@ export default {
     }
   }
 
-  > span > svg {
+  > span {
+    display: inline-block;
     cursor: pointer;
     z-index: 5;
-    margin-top: 10px;
+    margin-top: 7px;
     margin-left: 10px;
   }
 
   .session {
-    .fa-broadcast-tower {
     color: $demon;
     &.spectator {
       color: $townsfolk;
     }
   }
-  }
 }
 
 .menu {