Fix: UBSan division by zero runtime error in intern/shrinkwrap.cc

This error would occur because the quadratic equation solving code didn't
check for `a` being non-zero. Fixed by adding the additional check. This
can be tested and reproduced using the `ShrinkwrapTargetNormalProject2`
`modifiers` test.

Pull Request: https://projects.blender.org/blender/blender/pulls/133273

source/blender/blenkernel/intern/shrinkwrap.cc

@@ -956,7 +956,7 @@ static void target_project_edge(const ShrinkwrapTreeData *tree,
   float c = d0co - d0v0;
   float det = b * b - 4 * a * c;
 
-  if (det >= 0) {
+  if (det >= 0 && a != 0) {
     const float epsilon = 1e-6f;
     float sdet = sqrtf(det);
     float hit_co[3], hit_no[3];