fix fEntryCount when we purge a cache entry (bug caught by our validate())

git-svn-id: http://skia.googlecode.com/svn/trunk@712 2bbb7eff-a529-9590-31e7-b0007b416f81

src/effects/SkBitmapCache.cpp

@@ -107,9 +107,9 @@ void SkBitmapCache::add(const void* buffer, size_t len, const SkBitmap& bm) {
     AutoValidate av(this);
 
     if (fEntryCount == fMaxEntries) {
-        if (fTail) {
-            delete this->detach(fTail);
-        }
+        SkASSERT(fTail);
+        delete this->detach(fTail);
+        fEntryCount -= 1;
     }
 
     Entry* entry = new Entry(buffer, len, bm);