Fix a panic due to double-borrow

Cargo.toml

@@ -77,3 +77,6 @@ version = "0.8"
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 stdweb = { path = "../stdweb", optional = true }
 instant = { version = "0.1", features = ["stdweb"] }
+
+[patch.crates-io]
+stdweb = { path = "../stdweb" }

src/platform_impl/stdweb/event_loop.rs

@@ -333,9 +333,9 @@ impl<T: 'static> EventLoopRunnerShared<T> {
         }
 
         // Determine if event handling is in process, and then release the borrow on the runner
-        match *self.0.runner.borrow() {
+        let (start_cause, event_is_start) = match *self.0.runner.borrow() {
             Some(ref runner) if !runner.is_busy => {
-                let (start_cause, event_is_start) = if let Event::NewEvents(cause) = event {
+                if let Event::NewEvents(cause) = event {
                     (cause, true)
                 } else {
                     (match runner.control {
@@ -359,8 +359,16 @@ impl<T: 'static> EventLoopRunnerShared<T> {
                         },
                         ControlFlowStatus::Exit => { return; }
                     }, false)
+                }
+            }
+            _ => {
+                // Events are currently being handled, so queue this one and don't try to
+                // double-process the event queue
+                self.0.events.borrow_mut().push_back(event);
+                return;
+            }
         };
-                let mut control = runner.control.to_control_flow();
+        let mut control = self.current_control_flow();
         // Handle starting a new batch of events
         //
         // The user is informed via Event::NewEvents that there is a batch of events to process
@@ -370,20 +378,13 @@ impl<T: 'static> EventLoopRunnerShared<T> {
             self.handle_event(event, &mut control);
         }
         self.handle_event(Event::EventsCleared, &mut control);
-
         self.apply_control_flow(control);
-
         // If the event loop is closed, it has been closed this iteration and now the closing
         // event should be emitted
         if self.closed() {
             self.handle_event(Event::LoopDestroyed, &mut control);
         }
     }
-            _ => {
-                self.0.events.borrow_mut().push_back(event);
-            }
-        }
-    }
 
     // handle_event takes in events and either queues them or applies a callback
     //
@@ -464,5 +465,13 @@ impl<T: 'static> EventLoopRunnerShared<T> {
             None => false, // If the event loop is None, it has not been intialised yet, so it cannot be closed
         }
     }
+
+    // Get the current control flow state
+    fn current_control_flow(&self) -> ControlFlow {
+        match *self.0.runner.borrow() {
+            Some(ref runner) => runner.control.to_control_flow(),
+            None => ControlFlow::Poll,
+        }
+    }
 }