patch 8.2.2549: crash after using "g:" in a for loop

Problem:    Crash after using "g:" in a for loop.
Solution:   Increment the reference count. (closes #7892)
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index 3e69a0d..cda1ffd 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -2545,6 +2545,12 @@
   assert_equal('some', get(t:, 'some_var', 'xxx'))
   assert_equal('xxx', get(t:, 'no_var', 'xxx'))
   unlet t:some_var
+
+  # check using g: in a for loop more than DO_NOT_FREE_CNT times
+  for i in range(100000)
+    if has_key(g:, 'does-not-exist')
+    endif
+  endfor
 enddef
 
 def Test_expr7_parens()
diff --git a/src/version.c b/src/version.c
index 3d52e49..ff82645 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2549,
+/**/
     2548,
 /**/
     2547,
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 232f047..e20c711 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -1771,6 +1771,7 @@
 		    tv->v_type = VAR_DICT;
 		    tv->v_lock = 0;
 		    tv->vval.v_dict = d;
+		    ++d->dv_refcount;
 		    ++ectx.ec_stack.ga_len;
 		}
 		break;