vim-patch:8.2.4637: warning for using uninitialized variable

Problem:    Warning for using uninitialized variable. (Tony Mechelynck)
Solution:   Initialize it.

https://github.com/vim/vim/commit/565d1278cbbb7bc927bee207d5c2bc0bb95928fa

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/ex_docmd.c

@@ -2511,7 +2511,7 @@ static char *ex_range_without_command(exarg_T *eap)
 /// @return  FAIL when the command is not to be executed.
 int parse_command_modifiers(exarg_T *eap, const char **errormsg, cmdmod_T *cmod, bool skip_only)
 {
-  char *cmd_start;
+  char *cmd_start = NULL;
   bool has_visual_range = false;
   CLEAR_POINTER(cmod);