EngineFilterDelay: clamp wrong delay values

This commit moves the correctness evaluation of the delay value
into a setter and the set value is directly checked
instead of calculated index values.

src/engine/filters/enginefilterdelay.h

@@ -29,6 +29,15 @@ class EngineFilterDelay : public EngineObjectConstIn {
 
     void setDelay(unsigned int delaySamples) {
         m_delaySamples = delaySamples;
+
+        // When mixxx will support other channel count variants than stereo,
+        // the kMaxDelay has to be divisible by the number of channels.
+        // Otherwise, channels may be swapped.
+        const int maxDelaySamples = static_cast<int>(SIZE - mixxx::kEngineChannelCount);
+
+        VERIFY_OR_DEBUG_ASSERT(m_delaySamples <= maxDelaySamples) {
+            m_delaySamples = maxDelaySamples;
+        }
     }
 
     virtual void process(const CSAMPLE* pIn, CSAMPLE* pOutput,
@@ -41,15 +50,6 @@ class EngineFilterDelay : public EngineObjectConstIn {
             // (but in math the result value is positive).
             int delaySourcePos = (m_delayPos + SIZE - m_delaySamples) % SIZE;
 
-            VERIFY_OR_DEBUG_ASSERT(delaySourcePos >= 0) {
-                SampleUtil::copy(pOutput, pIn, iBufferSize);
-                return;
-            }
-            VERIFY_OR_DEBUG_ASSERT(delaySourcePos <= static_cast<int>(SIZE)) {
-                SampleUtil::copy(pOutput, pIn, iBufferSize);
-                return;
-            }
-
             for (int i = 0; i < iBufferSize; ++i) {
                 // put sample into delay buffer:
                 m_buf[m_delayPos] = pIn[i];
@@ -68,23 +68,6 @@ class EngineFilterDelay : public EngineObjectConstIn {
             int delaySourcePos = (m_delayPos + SIZE - m_delaySamples + iBufferSize / 2) % SIZE;
             int oldDelaySourcePos = (m_delayPos + SIZE - m_oldDelaySamples) % SIZE;
 
-            VERIFY_OR_DEBUG_ASSERT(delaySourcePos >= 0) {
-                SampleUtil::copy(pOutput, pIn, iBufferSize);
-                return;
-            }
-            VERIFY_OR_DEBUG_ASSERT(delaySourcePos <= static_cast<int>(SIZE)) {
-                SampleUtil::copy(pOutput, pIn, iBufferSize);
-                return;
-            }
-            VERIFY_OR_DEBUG_ASSERT(oldDelaySourcePos >= 0) {
-                SampleUtil::copy(pOutput, pIn, iBufferSize);
-                return;
-            }
-            VERIFY_OR_DEBUG_ASSERT(oldDelaySourcePos <= static_cast<int>(SIZE)) {
-                SampleUtil::copy(pOutput, pIn, iBufferSize);
-                return;
-            }
-
             double cross_mix = 0.0;
             double cross_inc = 2 / static_cast<double>(iBufferSize);