fix(ui): allow resize commands to set 'cmdheight' to 0

Resolve https://github.com/neovim/neovim/issues/21558

src/nvim/window.h

@@ -35,6 +35,8 @@
 #define MIN_COLUMNS     12      // minimal columns for screen
 #define MIN_LINES       2       // minimal lines for screen
 
+// Set to true if 'cmdheight' was explicitly set to 0.
+EXTERN bool p_ch_was_zero INIT(= false);
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "window.h.generated.h"
 #endif