fix overprotective GUI when switching to banks not present in current sf2

qtgui/mainwindow.py

@@ -297,8 +297,11 @@ class ChannelTreeItem(QtWidgets.QTreeWidgetItem):
 
     def _populateComboBox_Program(self, bank:int, program:int):
         self.comboBoxProgram.clear()
-        assert self.patchlist[bank] #not empty.
         assert 0 <=  program < 128, program
+        logger.info(f"populate: {bank}:{program}")
+        if not bank in self.patchlist:
+            logger.warning(f"Bank {bank} requested but not in sf2. Falling back to bank 0")
+            bank = 0
         nowProgram =  self.comboBoxProgram.currentIndex()  #if below fails at least we don't get an error. Worst case is the wrong label.
         for prgnr, patchname in self.patchlist[bank].items():
             #Not every program is in every bank. But we don' want a drop down list with gaps.
@@ -352,9 +355,8 @@ class ChannelTreeItem(QtWidgets.QTreeWidgetItem):
     def reactToBankOrProgramChange(self, newIndex): #discard newIndex
         bank = self.comboBoxBank.currentData()
         program = self.comboBoxProgram.currentData()
-        assert not bank is None, bank
-        assert not program is None, program
-        api.setPatch(self.channelNumber, bank, program) # triggers self.callback_channelChanged
+        if not bank is None and not program is None:
+            api.setPatch(self.channelNumber, bank, program) # triggers self.callback_channelChanged
 
     def callback_channelChanged(self, exportDict):
         """Either triggered by a GUI action, routed through the api, or by incoming midi message"""
@@ -364,7 +366,8 @@ class ChannelTreeItem(QtWidgets.QTreeWidgetItem):
 
         comboIndex = self.comboBoxBank.findData(exportDict["bank"])
         if comboIndex == -1: #qt for "not found"
-            raise ValueError("Bank not in patchlist")
+            #This was stupid. A bank change to a non-existing instrument is valid: raise ValueError("Bank not in patchlist")
+            pass
         else:
             self.comboBoxBank.setCurrentIndex(comboIndex) #both 0 based