Pattern: properly advance iterator when removing notes

We must not keep the iterator at the same position when erasing notes
from the m_notes array. This usually is not a problem when using QVector
but we might switch to QList somewhen later.

Signed-off-by: Tobias Doerffel <tobias.doerffel@gmail.com>

src/tracks/pattern.cpp

@@ -611,7 +611,7 @@ void pattern::changeTimeSignature( void )
 		if( ( *it )->length() == 0 && ( *it )->pos() >= last_pos )
 		{
 			delete *it;
-			m_notes.erase( it );
+			it = m_notes.erase( it );
 			--m_steps;
 		}
 		else