Fix repeated requests of reloading from disk

A popuped message appear for the 1st modification from outside of
Notepad++, if users ignore it and save another change outside, the 2nd
popuped message appears. This commit fix this bad behaviour, which could
lead crash.

Closes #3307

PowerEditor/src/ScitillaComponent/Buffer.cpp

@@ -250,7 +250,12 @@ bool Buffer::checkFileState() //eturns true if the status has been changed (it c
 
 			_currentStatus = DOC_MODIFIED;
 			_timeStamp = buf.st_mtime;
-			doNotify(BufferChangeStatus | BufferChangeReadonly | BufferChangeTimestamp);
+
+			if (_reloadFromDiskRequestGuard.try_lock())
+			{
+				doNotify(BufferChangeStatus | BufferChangeReadonly | BufferChangeTimestamp);
+				_reloadFromDiskRequestGuard.unlock();
+			}
 			isOK = true;
 		}
 	}
@@ -273,10 +278,17 @@ bool Buffer::checkFileState() //eturns true if the status has been changed (it c
 
 		if (mask != 0)
 		{
-			doNotify(mask);
-			isOK = true;
+			if (_reloadFromDiskRequestGuard.try_lock())
+			{
+				doNotify(mask);
+
+				_reloadFromDiskRequestGuard.unlock();
+
+				return true;
+			}
 		}
-		isOK = false;
+
+		return false;
 	}
 
 	if (isWow64Off)

PowerEditor/src/ScitillaComponent/Buffer.h

@@ -25,6 +25,8 @@
 // along with this program; if not, write to the Free Software
 // Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 #pragma once
+#include <mutex>
+
 #include "Utf8_16.h"
 
 
@@ -413,4 +415,6 @@ private:
 	bool _hasLangBeenSetFromMenu = false;
 
 	MapPosition _mapPosition;
+
+	std::mutex _reloadFromDiskRequestGuard;
 };