Call the should_fail_common check earlier

This avoids parsing a prefix when the message came from a bot or webhook.

src/framework/standard/mod.rs

@@ -616,6 +616,14 @@ impl StandardFramework {
 impl Framework for StandardFramework {
     #[instrument(skip(self, ctx))]
     async fn dispatch(&self, mut ctx: Context, msg: Message) {
+        if let Some(error) = self.should_fail_common(&msg) {
+            if let Some(dispatch) = &self.dispatch {
+                dispatch(&mut ctx, &msg, error).await;
+            }
+
+            return;
+        }
+
         let mut stream = Stream::new(&msg.content);
 
         stream.take_while_char(|c| c.is_whitespace());
@@ -638,14 +646,6 @@ impl Framework for StandardFramework {
             return;
         }
 
-        if let Some(error) = self.should_fail_common(&msg) {
-            if let Some(dispatch) = &self.dispatch {
-                dispatch(&mut ctx, &msg, error).await;
-            }
-
-            return;
-        }
-
         let invocation = parse::command(
             &ctx,
             &msg,