Simplify InsertOrReplaceRelative, always trim when to domain...

... Comment in it says that it does not check for discontinuities if it
replaces!

This will not matter in the uses of it internal to the Envelope class, which
will in fact always be proper insertions, having checked first for the presence
of a point.

src/Envelope.cpp

@@ -1107,35 +1107,20 @@ int Envelope::InsertOrReplaceRelative(double when, double value)
 #endif
 
    int len = mEnv.size();
+   when = std::max( 0.0, std::min( mTrackLen, when ) );
 
-   if (len && when < 0.0)
-      return 0;
-   if ((len > 1) && when > mTrackLen)
-      return len - 1;
+   auto range = EqualRange( when, 0 );
+   int index = range.first;
 
-   if (when < 0.0)
-      when = 0.0;
-   if ((len>1) && when > mTrackLen)
-      when = mTrackLen;
-
-   int i = 0;
-
-   while (i < len && when > mEnv[i].GetT())
-      i++;
-
-   if(i < len && when == mEnv[i].GetT())
-     // modify existing
-     mEnv[i].SetVal( this, value );
-   else {
+   if ( index < range.second )
+      // modify existing
+      // In case of a discontinuity, ALWAYS CHANGING LEFT LIMIT ONLY!
+      mEnv[ index ].SetVal( this, value );
+   else
      // Add NEW
-     EnvPoint e{ when, value };
-     if (i < len) {
-        Insert(i, e);
-     } else {
-        mEnv.push_back(e);
-     }
-   }
-   return i;
+      Insert( index, EnvPoint { when, value } );
+
+   return index;
 }
 
 std::pair<int, int> Envelope::EqualRange( double when, double sampleDur ) const

src/Envelope.h

@@ -196,6 +196,7 @@ public:
 
 private:
    int InsertOrReplaceRelative(double when, double value);
+
    friend class EnvelopeEditor;
    /** \brief Accessor for points */
    const EnvPoint &operator[] (int index) const