Improve error message when bundled resource could not found. (#328)

A team member of mine spend a couple of hours debugging this error:
Couldn't find com.facebook.react.uimanager.annotations.ReactProp.source.

There was no clear indicator of what the underlaying problem was. As it turns out the error was caused by missing assets. To make sure other developers don't waste the same amount of time as we did, we improved the error message.

android/src/main/java/com/dylanvann/fastimage/FastImageSource.java

@@ -1,7 +1,9 @@
 package com.dylanvann.fastimage;
 
 import android.content.Context;
+import android.content.res.Resources;
 import android.net.Uri;
+import android.text.TextUtils;
 
 import com.bumptech.glide.load.model.GlideUrl;
 import com.bumptech.glide.load.model.Headers;
@@ -37,7 +39,6 @@ public FastImageSource(Context context, String source) {
         this(context, source, null);
     }
 
-
     public FastImageSource(Context context, String source, @Nullable Headers headers) {
         this(context, source, 0.0d, 0.0d, headers);
     }
@@ -47,6 +48,10 @@ public FastImageSource(Context context, String source, double width, double heig
         mHeaders = headers == null ? Headers.DEFAULT : headers;
         mUri = super.getUri();
 
+        if (isResource() && TextUtils.isEmpty(mUri.toString())) {
+            throw new Resources.NotFoundException("Local Resource Not Found. Resource: '" + getSource() + "'.");
+        }
+
         if (isLocalResourceUri(mUri)) {
             // Convert res:/ scheme to android.resource:// so
             // glide can understand the uri.