fix [3148312] Region can access data out of bounds

Change-Id: Ic46f31d40943f405e37da21a50b55edd5a2c4124
diff --git a/libs/ui/Region.cpp b/libs/ui/Region.cpp
index 12db908..1994f6a 100644
--- a/libs/ui/Region.cpp
+++ b/libs/ui/Region.cpp
@@ -289,7 +289,7 @@
     void flushSpan() {
         bool merge = false;
         if (tail-head == ssize_t(span.size())) {
-            Rect const* p = cur;
+            Rect const* p = span.editArray();
             Rect const* q = head;
             if (p->top == q->bottom) {
                 merge = true;