fix(api): vim.cmd.make crashes when argument count isn't 1 (#19701)

Closes #19696

src/nvim/api/command.c

@@ -819,11 +819,14 @@ static void build_cmdline_str(char **cmdlinep, exarg_T *eap, CmdParseInfo *cmdin
   char *p = replace_makeprg(eap, eap->arg, cmdlinep);
   if (p != eap->arg) {
     // If replace_makeprg modified the cmdline string, correct the argument pointers.
-    assert(argc == 1);
     eap->arg = p;
+    // We can only know the position of the first argument because the argument list can be used
+    // multiple times in makeprg / grepprg.
+    if (argc >= 1) {
       eap->args[0] = p;
     }
   }
+}
 
 /// Create a new user command |user-commands|
 ///

test/functional/api/vim_spec.lua

@@ -3829,5 +3829,12 @@ describe('API', function()
       eq({'aa'}, meths.buf_get_lines(0, 0, 1, false))
       assert_alive()
     end)
+    it("'make' command works when argument count isn't 1 #19696", function()
+      command('set makeprg=echo')
+      meths.cmd({ cmd = 'make' }, {})
+      assert_alive()
+      meths.cmd({ cmd = 'make', args = { 'foo', 'bar' } }, {})
+      assert_alive()
+    end)
   end)
 end)