patch 8.2.1037: Vim9: crash when using line continuation inside :def

Problem:    Vim9: crash when using line continuation inside :def.
Solution:   Check for no more lines available.
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 6a9d4ba..fbe73f7 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -837,5 +837,16 @@
   res = [1, 2, 3]->sort()
 enddef
 
+def Line_continuation_in_def(dir: string = ''): string
+    let path: string = empty(dir)
+            \ ? 'empty'
+            \ : 'full'
+    return path
+enddef
+
+def Test_line_continuation_in_def()
+  assert_equal('full', Line_continuation_in_def('.'))
+enddef
+
 
 " vim: ts=8 sw=2 sts=2 expandtab tw=80 fdm=marker
diff --git a/src/version.c b/src/version.c
index 42c03d0..43b1010 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1037,
+/**/
     1036,
 /**/
     1035,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 033a8d9..30e447f 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -2402,8 +2402,11 @@
     while (++lnum < cctx->ctx_ufunc->uf_lines.ga_len)
     {
 	char_u *line = ((char_u **)cctx->ctx_ufunc->uf_lines.ga_data)[lnum];
-	char_u *p = skipwhite(line);
+	char_u *p;
 
+	if (line == NULL)
+	    break;
+	p = skipwhite(line);
 	if (*p != NUL && !comment_start(p))
 	    return p;
     }