[core] Fixed CUnitQueue::getNextAvailUnit(..)

Refers to issue Haivision#486 getting available uit to receive a packet

srtcore/queue.cpp

@@ -216,24 +216,28 @@ CUnit *CUnitQueue::getNextAvailUnit()
     if (m_iCount >= m_iSize)
         return NULL;
 
-    CQEntry *entrance = m_pCurrQueue;
-
+    int units_checked = 0;
     do
     {
-        for (CUnit *sentinel = m_pCurrQueue->m_pUnit + m_pCurrQueue->m_iSize - 1; m_pAvailUnit != sentinel;
-             ++m_pAvailUnit)
+        CUnit *lastunit = m_pCurrQueue->m_pUnit + m_pCurrQueue->m_iSize - 1;
+        for (; m_pAvailUnit != lastunit; ++m_pAvailUnit, ++units_checked)
+        {
             if (m_pAvailUnit->m_iFlag == CUnit::FREE)
+            {
                 return m_pAvailUnit;
+            }
+        }
 
-        if (m_pCurrQueue->m_pUnit->m_iFlag == CUnit::FREE)
+        if (lastunit->m_iFlag == CUnit::FREE)
         {
-            m_pAvailUnit = m_pCurrQueue->m_pUnit;
+            m_pAvailUnit = lastunit;
             return m_pAvailUnit;
         }
 
+        ++units_checked;
         m_pCurrQueue = m_pCurrQueue->m_pNext;
         m_pAvailUnit = m_pCurrQueue->m_pUnit;
-    } while (m_pCurrQueue != entrance);
+    } while (units_checked < m_iSize);
 
     increase();