patch 8.2.1914: Vim9: cannot put line break in expression for '=' register

Problem:    Vim9: cannot put line break in expression for '=' register.
Solution:   Pass fgetline to set_expr_line(). (closes #7209)
diff --git a/src/misc2.c b/src/misc2.c
index 6316b53..48cc4b7 100644
--- a/src/misc2.c
+++ b/src/misc2.c
@@ -1131,7 +1131,7 @@
     free_signs();
 # endif
 # ifdef FEAT_EVAL
-    set_expr_line(NULL);
+    set_expr_line(NULL, NULL);
 # endif
 # ifdef FEAT_DIFF
     if (curtab != NULL)