patch 8.2.1972: crash when recreating nested fold

Problem:    Crash when recreating nested fold.
Solution:   Check for empty growarray. (closes #7278)
diff --git a/src/fold.c b/src/fold.c
index 4b4e618..82ce7e7 100644
--- a/src/fold.c
+++ b/src/fold.c
@@ -640,7 +640,10 @@
 		break;
 	    }
 	}
-	i = (int)(fp - (fold_T *)gap->ga_data);
+	if (gap->ga_len == 0)
+	    i = 0;
+	else
+	    i = (int)(fp - (fold_T *)gap->ga_data);
     }
 
     if (ga_grow(gap, 1) == OK)
diff --git a/src/testdir/test_fold.vim b/src/testdir/test_fold.vim
index f0bd6e4..1377983 100644
--- a/src/testdir/test_fold.vim
+++ b/src/testdir/test_fold.vim
@@ -844,4 +844,14 @@
   bwipe!
 endfunc
 
+" this was crashing
+func Test_fold_create_delete_create()
+  new
+  fold
+  fold
+  normal zd
+  fold
+  bwipe!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index 91477bc..e2affa7 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1972,
+/**/
     1971,
 /**/
     1970,