Fix AddressSanitizer: heap-buffer-overflow caused by incorrect padding

Fixes godotengine#94548

Use reserve() instead of resize() when padding the buffer passed to
embree, otherwise it will look past the end of the buffer since we pass
the size() to rtcSetSharedGeometryBuffer and it dereferences
`(int*)getPtr(size()-1) + 3`
could cause a segfault if `capacity < size + 12`(bytes)

When the address sanitizer is enabled it triggers an assertion

    /*! checks padding to 16 byte check, fails hard */
    __forceinline void checkPadding16() const
    {
      if (ptr_ofs && num)
volatile int MAYBE_UNUSED w = *((int*)getPtr(size()-1)+3); //
FIXME: is failing hard avoidable?
    }

Author: jamie-pate

modules/raycast/raycast_occlusion_cull.cpp

@@ -349,9 +349,11 @@ void RaycastOcclusionCull::Scenario::_update_dirty_instance(int p_idx, RID *p_in
 	}
 
 	int vertices_size = occ->vertices.size();
-
+	occ_inst->xformed_vertices.resize(vertices_size);
 	// Embree requires the last element to be readable by a 16-byte SSE load instruction, so we add padding to be safe.
-	occ_inst->xformed_vertices.resize(vertices_size + 1);
+	const size_t byte_padding = sizeof(int) * 3;
+	const size_t vertices_padding = ceil((float)byte_padding / (float)sizeof(Vector3));
+	occ_inst->xformed_vertices.reserve(vertices_size + vertices_padding);
 
 	const Vector3 *read_ptr = occ->vertices.ptr();
 	Vector3 *write_ptr = occ_inst->xformed_vertices.ptr();