fix gcc optimized build

../sql/spatial.cc: In member function ‘double Gis_point::calculate_haversine(const Geometry*, double, int*)’:
../sql/spatial.cc:1093:45: error: ‘y1r’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
 1093 |   res= 2*sphere_radius*asin((sqrt(dlat + cos(y1r)*cos(y2r)*dlong)));
      |                                          ~~~^~~~~
../sql/spatial.cc:1092:20: error: ‘x1r’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
 1092 |   dlong=  sin((x2r - x1r)/2)*sin((x2r - x1r)/2);
      |               ~~~~~^~~~~~
../sql/spatial.cc:1093:54: error: ‘y2r’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
 1093 |   res= 2*sphere_radius*asin((sqrt(dlat + cos(y1r)*cos(y2r)*dlong)));
      |                                                   ~~~^~~~~
../sql/spatial.cc:1092:20: error: ‘x2r’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
 1092 |   dlong=  sin((x2r - x1r)/2)*sin((x2r - x1r)/2);
      |               ~~~~~^~~~~~
c

sql/spatial.cc

@@ -1050,7 +1050,7 @@ double Gis_point::calculate_haversine(const Geometry *g,
                                       int *error)
 {
   DBUG_ASSERT(sphere_radius > 0);
-  double x1r, x2r, y1r, y2r, dlong, dlat, res;
+  double x1r= 0.0, x2r= 0.0, y1r= 0.0, y2r= 0.0, dlong, dlat, res;
 
   // This check is done only for optimization purposes where we know it will
   // be one and only one point in Multipoint