Replace if (ga->ga_len) with if (!GA_EMPTY(ga))

Used Coccinelle to perform the changes

```diff
@@
expression E;
statement S;
@@

(
- if (E.ga_len) S
+ if (!GA_EMPTY(&E)) S
|
- if (E->ga_len) S
+ if (!GA_EMPTY(E)) S
)
```

1 files changed, 2 insertions, 2 deletions

diff --git a/src/nvim/syntax.c b/src/nvim/syntax.c
index c1fb1d50ba..a72bd2bec6 100644
--- a/src/nvim/syntax.c
+++ b/src/nvim/syntax.c
@@ -892,7 +892,7 @@ static void syn_sync(win_T *wp, linenr_T start_lnum, synstate_T *last_valid)
          * For "groupthere" the parsing starts at start_lnum.
          */
         if (found_flags & HL_SYNC_HERE) {
-          if (current_state.ga_len) {
+          if (!GA_EMPTY(&current_state)) {
             cur_si = &CUR_STATE(current_state.ga_len - 1);
             cur_si->si_h_startpos.lnum = found_current_lnum;
             cur_si->si_h_startpos.col = found_current_col;
@@ -2595,7 +2595,7 @@ static void push_current_state(int idx)
  */
 static void pop_current_state(void)
 {
-  if (current_state.ga_len) {
+  if (!GA_EMPTY(&current_state)) {
     unref_extmatch(CUR_STATE(current_state.ga_len - 1).si_extmatch);
     --current_state.ga_len;
   }