Improve error handling when saving

Report any errors that might occur while saving changes to the database
to the user. Also warn the user that this means the database wasn't
saved entirely.

See issue sqlitebrowser#770.

Author: MKleusberg

src/MainWindow.cpp

@@ -1113,7 +1113,13 @@ void MainWindow::dbState( bool dirty )
 void MainWindow::fileSave()
 {
     if(db.isOpen())
-        db.releaseAllSavepoints();
+    {
+        if(!db.releaseAllSavepoints())
+        {
+            QMessageBox::warning(this, QApplication::applicationName(), tr("Error while saving the database file. This means that not all changes to the database were "
+                                                                           "saved. You need to resolve the following error first.\n\n%1").arg(db.lastErrorMessage));
+        }
+    }
 }
 
 void MainWindow::fileRevert()

src/sqlitedb.cpp

@@ -288,7 +288,8 @@ bool DBBrowserDB::releaseSavepoint(const QString& pointname)
         return false;
 
     QString query = QString("RELEASE %1;").arg(pointname);
-    executeSQL(query, false, false);
+    if(!executeSQL(query, false, false))
+        return false;
     savepointList.removeAll(pointname);
     emit dbChanged(getDirty());