patch 9.1.0993: New 'cmdheight' behavior may be surprising

patch 9.1.0993: New 'cmdheight' behavior may be surprising

Problem:  Although patch 9.1.0990 fixed a real problem/inconsistency,
          it also introduced new behavior that may break BWC and/or be
          unexpected. Before 9.1.0990, window commands could make the
          topframe smaller (without changing 'cmdheight'; quirk that is
          now fixed), but did not allow extending the topframe beyond
          the 'cmdheight' set by the user. After 9.1.0990, the user can
          reduce the 'cmdheight' below the value they set explicitly,
          through window commands, which may lead to confusion.
          (aftere v9.1.0990)
Solution: Store the value explicitly set by the user and clamp the
          'cmdheight' when resizing the topframe. This also applies to
          dragging laststatus, which in contrast to window commands
          _did_ allow reducing the 'cmdheight' to values below the one
          set by the user. So with this patch there is still new
          behavior, but I think in a way that is less surprising.
          While at it, also fix a Coverity warning, introduced in
          v9.1.0990 (Luuk van Baal)

closes: #16385

Signed-off-by: Luuk van Baal <luukvbaal@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>