refactor: fix clang NonNullParamChecker warnings (#28327)

src/nvim/CMakeLists.txt

@@ -844,7 +844,6 @@ add_glob_target(
   --checks='
   -*,
   clang-analyzer-*,
-  -clang-analyzer-core.NonNullParamChecker,
   -clang-analyzer-core.NullDereference,
   -clang-analyzer-core.UndefinedBinaryOperatorResult,
   -clang-analyzer-core.uninitialized.Assign,

src/nvim/regexp.c

@@ -5320,7 +5320,7 @@ static regprog_T *bt_regcomp(uint8_t *expr, int re_flags)
   }
   // Remember whether this pattern has any \z specials in it.
   r->reghasz = (uint8_t)re_has_z;
-  scan = r->program + 1;        // First BRANCH.
+  scan = &r->program[1];  // First BRANCH.
   if (OP(regnext(scan)) == END) {   // Only one top-level choice.
     scan = OPERAND(scan);
 
@@ -7322,7 +7322,7 @@ static int regtry(bt_regprog_T *prog, colnr_T col, proftime_T *tm, int *timed_ou
   // Clear the external match subpointers if necessaey.
   rex.need_clear_zsubexpr = (prog->reghasz == REX_SET);
 
-  if (regmatch(prog->program + 1, tm, timed_out) == 0) {
+  if (regmatch(&prog->program[1], tm, timed_out) == 0) {
     return 0;
   }
 
@@ -7664,7 +7664,7 @@ static void regdump(uint8_t *pattern, bt_regprog_T *r)
   fprintf(f, "-------------------------------------\n\r\nregcomp(%s):\r\n",
           pattern);
 
-  s = r->program + 1;
+  s = &r->program[1];
   // Loop until we find the END that isn't before a referred next (an END
   // can also appear in a NOMATCH operand).
   while (op != END || s <= end) {

src/nvim/window.c

@@ -1959,6 +1959,7 @@ int win_splitmove(win_T *wp, int size, int flags)
     // Remove the window and frame from the tree of frames.  Don't flatten any
     // frames yet so we can restore things if win_split_ins fails.
     winframe_remove(wp, &dir, NULL, &unflat_altfr);
+    assert(unflat_altfr != NULL);
     win_remove(wp, NULL);
     last_status(false);  // may need to remove last status line
     win_comp_pos();  // recompute window positions
@@ -1967,6 +1968,7 @@ int win_splitmove(win_T *wp, int size, int flags)
   // Split a window on the desired side and put "wp" there.
   if (win_split_ins(size, flags, wp, dir, unflat_altfr) == NULL) {
     if (!wp->w_floating) {
+      assert(unflat_altfr != NULL);
       // win_split_ins doesn't change sizes or layout if it fails to insert an
       // existing window, so just undo winframe_remove.
       winframe_restore(wp, dir, unflat_altfr);