Avoid useless computations when determinant is 0

Change-Id: I8b9fcb995116068fdaed26f3a7b084b154ea3bc1

av1/common/warped_motion.c

diff --git a/av1/common/warped_motion.c b/av1/common/warped_motion.c
index 8be9e71..f9b5cf7 100644
--- a/av1/common/warped_motion.c
+++ b/av1/common/warped_motion.c
@@ -1166,15 +1166,9 @@
   assert(By[0] >= LS_MAT_MIN && By[0] <= LS_MAT_MAX);
   assert(By[1] >= LS_MAT_MIN && By[1] <= LS_MAT_MAX);
 
-  int64_t Px[2], Py[2], Det;
+  int64_t Det;
   int16_t iDet, shift;
 
-  // These divided by the Det, are the least squares solutions
-  Px[0] = (int64_t)A[1][1] * Bx[0] - (int64_t)A[0][1] * Bx[1];
-  Px[1] = -(int64_t)A[0][1] * Bx[0] + (int64_t)A[0][0] * Bx[1];
-  Py[0] = (int64_t)A[1][1] * By[0] - (int64_t)A[0][1] * By[1];
-  Py[1] = -(int64_t)A[0][1] * By[0] + (int64_t)A[0][0] * By[1];
-
   // Compute Determinant of A
   Det = (int64_t)A[0][0] * A[1][1] - (int64_t)A[0][1] * A[0][1];
   if (Det == 0) return 1;
@@ -1185,6 +1179,14 @@
     shift = 0;
   }
 
+  int64_t Px[2], Py[2];
+
+  // These divided by the Det, are the least squares solutions
+  Px[0] = (int64_t)A[1][1] * Bx[0] - (int64_t)A[0][1] * Bx[1];
+  Px[1] = -(int64_t)A[0][1] * Bx[0] + (int64_t)A[0][0] * Bx[1];
+  Py[0] = (int64_t)A[1][1] * By[0] - (int64_t)A[0][1] * By[1];
+  Py[1] = -(int64_t)A[0][1] * By[0] + (int64_t)A[0][0] * By[1];
+
   wm->wmmat[2] = get_mult_shift_diag(Px[0], iDet, shift);
   wm->wmmat[3] = get_mult_shift_ndiag(Px[1], iDet, shift);
   wm->wmmat[4] = get_mult_shift_ndiag(Py[0], iDet, shift);