Simplify KeyError fallbacks that don't need to be lazy

[Avasam]

This also avoids touching error re-raising.

By "lazy" I mean that for example in com/win32comext/axdebug/codecontainer.py:

    def GetCodeContextAtPosition(self, charPos):
        # Convert to line number.
        lineNo, offset = self.GetLineOfPosition(charPos)
        charPos = self.GetPositionOfLine(lineNo)
        try:
            cc = self.codeContexts[charPos]
        except KeyError:
            cc = self._MakeContextAtPosition(charPos)
            self.codeContexts[charPos] = cc
        return cc

Can't be simplified to:

    def GetCodeContextAtPosition(self, charPos):
        # Convert to line number.
        lineNo, offset = self.GetLineOfPosition(charPos)
        charPos = self.GetPositionOfLine(lineNo)
        return self.codeContexts.setdefault(charPos, self._MakeContextAtPosition(charPos))

because it would needlessly call self._MakeContextAtPosition(charPos) early