fix(modeld): Fix for unpredictable behavior in commonmodel_pyx.pyx (#32482)

Avoid undefined behavior

Co-authored-by: 19igari <koki.igari@turing-motors.com>

selfdrive/modeld/models/commonmodel_pyx.pyx

@@ -37,7 +37,11 @@ cdef class ModelFrame:
   def prepare(self, VisionBuf buf, float[:] projection, CLMem output):
     cdef mat3 cprojection
     memcpy(cprojection.v, &projection[0], 9*sizeof(float))
-    cdef float * data = self.frame.prepare(buf.buf.buf_cl, buf.width, buf.height, buf.stride, buf.uv_offset, cprojection, output.mem)
+    cdef float * data
+    if output is None:
+      data = self.frame.prepare(buf.buf.buf_cl, buf.width, buf.height, buf.stride, buf.uv_offset, cprojection, NULL)
+    else:
+      data = self.frame.prepare(buf.buf.buf_cl, buf.width, buf.height, buf.stride, buf.uv_offset, cprojection, output.mem)
     if not data:
       return None
     return np.asarray(<cnp.float32_t[:self.frame.buf_size]> data)