Changed Qt debugger data save file extension to be .fdb instead of .dbg so that it does not conflict/overwrite ld65 debug symbol files. Fixes issue #600.

src/drivers/Qt/ConsoleDebugger.cpp

@@ -4374,9 +4374,9 @@ static int getGameDebugBreakpointFileName(char *filepath)
 	}
 
 	filepath[i] = '.'; i++;
+	filepath[i] = 'f'; i++;
 	filepath[i] = 'd'; i++;
 	filepath[i] = 'b'; i++;
-	filepath[i] = 'g'; i++;
 	filepath[i] =  0;
 
 	return 0;