patch 8.2.4813: pasting text while indent folding may mess up folds

Problem:    Pasting text while indent folding may mess up folds.
Solution:   Adjust the way folds are split. (Brandon Simmons, closes #10254)
diff --git a/src/fold.c b/src/fold.c
index 8078e3a..229cb2a 100644
--- a/src/fold.c
+++ b/src/fold.c
@@ -1128,7 +1128,7 @@
 // foldFind() {{{2
 /*
  * Search for line "lnum" in folds of growarray "gap".
- * Set *fpp to the fold struct for the fold that contains "lnum" or
+ * Set "*fpp" to the fold struct for the fold that contains "lnum" or
  * the first fold below it (careful: it can be beyond the end of the array!).
  * Returns FALSE when there is no fold that contains "lnum".
  */
@@ -2911,7 +2911,8 @@
     // any between top and bot, they have been removed by the caller.
     gap1 = &fp->fd_nested;
     gap2 = &fp[1].fd_nested;
-    if (foldFind(gap1, bot + 1 - fp->fd_top, &fp2))
+    (void)foldFind(gap1, bot + 1 - fp->fd_top, &fp2);
+    if (fp2 != NULL)
     {
 	len = (int)((fold_T *)gap1->ga_data + gap1->ga_len - fp2);
 	if (len > 0 && ga_grow(gap2, len) == OK)