fix Region const_iterator.

- it returned an empty rect when the region was empty, instead
of returning an empty list of rect.

- also fixed an infinite loop when boolean_operation was given
an empty list of rects

Change-Id: I62225c7dcd2832025bb8f12e6cb3762f2a7b36cb

include/private/ui/RegionHelper.h

@@ -96,6 +96,11 @@ private:
     class SpannerBase
     {
     public:
+        SpannerBase()
+            : lhs_head(max_value), lhs_tail(max_value),
+              rhs_head(max_value), rhs_tail(max_value) {
+        }
+
         enum {
             lhs_before_rhs   = 0,
             lhs_after_rhs    = 1,
@@ -160,11 +165,15 @@ private:
         inline Spanner(const region& lhs, const region& rhs)
         : lhs(lhs), rhs(rhs)
         {
+            if (lhs.count) {
                 SpannerBase::lhs_head = lhs.rects->top      + lhs.dy;
                 SpannerBase::lhs_tail = lhs.rects->bottom   + lhs.dy;
+            }
+            if (rhs.count) {
                 SpannerBase::rhs_head = rhs.rects->top      + rhs.dy;
                 SpannerBase::rhs_tail = rhs.rects->bottom   + rhs.dy;
             }
+        }
 
         inline bool isDone() const {
             return !rhs.count && !lhs.count;
@@ -221,22 +230,30 @@ private:
 
         inline void prepare(int inside) {
             if (inside == SpannerBase::lhs_before_rhs) {
+                if (lhs.count) {
                     SpannerBase::lhs_head = lhs.rects->left  + lhs.dx;
                     SpannerBase::lhs_tail = lhs.rects->right + lhs.dx;
+                }
                 SpannerBase::rhs_head = max_value;
                 SpannerBase::rhs_tail = max_value;
             } else if (inside == SpannerBase::lhs_after_rhs) {
                 SpannerBase::lhs_head = max_value;
                 SpannerBase::lhs_tail = max_value;
+                if (rhs.count) {
                     SpannerBase::rhs_head = rhs.rects->left  + rhs.dx;
                     SpannerBase::rhs_tail = rhs.rects->right + rhs.dx;
+                }
             } else {
+                if (lhs.count) {
                     SpannerBase::lhs_head = lhs.rects->left  + lhs.dx;
                     SpannerBase::lhs_tail = lhs.rects->right + lhs.dx;
+                }
+                if (rhs.count) {
                     SpannerBase::rhs_head = rhs.rects->left  + rhs.dx;
                     SpannerBase::rhs_tail = rhs.rects->right + rhs.dx;
                 }
             }
+        }
 
         inline bool isDone() const {
             return SpannerBase::lhs_head == max_value && 

libs/ui/Region.cpp

@@ -619,7 +619,15 @@ Region::const_iterator Region::begin() const {
 }
 
 Region::const_iterator Region::end() const {
-    return isRect() ? ((&mBounds) + 1) : (mStorage.array() + mStorage.size());
+    if (isRect()) {
+        if (isEmpty()) {
+            return &mBounds;
+        } else {
+            return &mBounds + 1;
+        }
+    } else {
+        return mStorage.array() + mStorage.size();
+    }
 }
 
 Rect const* Region::getArray(size_t* count) const {