rlottie/trim: Fix trim segment calculation.

In AE start and end value can naver be -ve. but the final
start and end value after applting interpolator curve could be -ve.

So refactor to always take the -ve value into account.

src/lottie/lottiemodel.h

@@ -768,10 +768,6 @@ public:
         if (vCompare(diff, 0.0f)) return Segment(0, 0);
         if (vCompare(diff, 1.0f)) return Segment(0, 1);
 
-        // no offset case
-        if (vCompare(fabs(offset), 0.0f)) {
-            return noloop(start, end);
-        } else {
         if (offset > 0) {
             start += offset;
             end += offset;
@@ -789,23 +785,26 @@ public:
             if (start >= 0 && end >= 0) {
                 return noloop(start, end);
             } else if (start < 0 && end < 0) {
-                    return noloop(-start, -end);
+                return noloop(1 + start, 1 + end);
             } else {
                 if (start < 0) return loop(1 + start, end);
                 else return loop(start , 1 + end);
             }
         }
     }
-    }
     LOTTrimData::TrimType type() const {return mTrimType;}
 private:
     Segment noloop(float start, float end) const{
+        assert(start >= 0);
+        assert(end >= 0);
         Segment s;
         s.start = std::min(start, end);
         s.end = std::max(start, end);
         return s;
     }
     Segment loop(float start, float end) const{
+        assert(start >= 0);
+        assert(end >= 0);
         Segment s;
         s.start = std::max(start, end);
         s.end = std::min(start, end);