libyang MAINTENANCE change format of the empty loops

To improve readability and because of processing by the formatting
tools, add explicit empty block to the empty loops (for, while).
diff --git a/src/diff.c b/src/diff.c
index 595957f..09ea1fb 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -199,7 +199,7 @@
         if (first->parent) {
             iter = first->parent->child;
         } else {
-            for (iter = first; iter->prev->next; iter = iter->prev);
+            for (iter = first; iter->prev->next; iter = iter->prev) {}
         }
         for (; iter; iter = iter->next) {
             if (iter->schema == first->schema) {