Fix locking scheme for double-clicks

In some cases, the events may be driven in the same thread, which can
lead to a deadlock.  Instead of waiting for the lock, simply refuse to
run if a loading system in in progress.

Fixes #6606

kicad/mainframe.cpp

@@ -317,7 +317,10 @@ void KICAD_MANAGER_FRAME::RunEeschema( const wxString& aProjectSchematicFileName
     KIWAY_PLAYER* frame;
 
     // Prevent multiple KiFace loading at one time
-    const std::lock_guard<std::mutex> lock( m_loading );
+    if( !m_loading.try_lock() )
+        return;
+
+    const std::lock_guard<std::mutex> lock( m_loading, std::adopt_lock );
 
     try
     {
@@ -365,7 +368,10 @@ void KICAD_MANAGER_FRAME::OnRunSchLibEditor( wxCommandEvent& event )
     KIWAY_PLAYER* frame;
 
     // Prevent multiple KiFace loading at one time
-    const std::lock_guard<std::mutex> lock( m_loading );
+    if( !m_loading.try_lock() )
+        return;
+
+    const std::lock_guard<std::mutex> lock( m_loading, std::adopt_lock );
 
     try
     {
@@ -394,7 +400,10 @@ void KICAD_MANAGER_FRAME::RunPcbNew( const wxString& aProjectBoardFileName )
     KIWAY_PLAYER* frame;
 
     // Prevent multiple KiFace loading at one time
-    const std::lock_guard<std::mutex> lock( m_loading );
+    if( !m_loading.try_lock() )
+        return;
+
+    const std::lock_guard<std::mutex> lock( m_loading, std::adopt_lock );
 
     try
     {
@@ -440,7 +449,10 @@ void KICAD_MANAGER_FRAME::OnRunPcbFpEditor( wxCommandEvent& event )
     KIWAY_PLAYER* frame;
 
     // Prevent multiple KiFace loading at one time
-    const std::lock_guard<std::mutex> lock( m_loading );
+    if( !m_loading.try_lock() )
+        return;
+
+    const std::lock_guard<std::mutex> lock( m_loading, std::adopt_lock );
 
     try
     {