Replace ga->ga_len > 0 checks with !GA_EMPTY(ga)

Used Coccinelle to perform the changes

```diff
@@
expression E;
@@

<...
(
- E.ga_len > 0
+ !GA_EMPTY(&E)
|
- E->ga_len > 0
+ !GA_EMPTY(E)
)
...>
```

`spatch --in-place --sp-file ga_empty.cocci <C_FILE>`

1 files changed, 2 insertions, 2 deletions

diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index 268e625b48..368d5c9b0c 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -872,7 +872,7 @@ int flags;
      * When not inside any ":while" loop, clear remembered lines.
      */
     if (cstack.cs_looplevel == 0) {
-      if (lines_ga.ga_len > 0) {
+      if (!GA_EMPTY(&lines_ga)) {
         sourcing_lnum =
           ((wcmd_T *)lines_ga.ga_data)[lines_ga.ga_len - 1].lnum;
         free_cmdlines(&lines_ga);
@@ -1188,7 +1188,7 @@ static void store_loop_line(garray_T *gap, char_u *line)
  */
 static void free_cmdlines(garray_T *gap)
 {
-  while (gap->ga_len > 0) {
+  while (!GA_EMPTY(gap)) {
     free(((wcmd_T *)(gap->ga_data))[gap->ga_len - 1].line);
     --gap->ga_len;
   }