Guard against casting a double NaN to an int. We don't care what value

is returned; however, reportedly, a program can crash in this case, see

  OSGeo/PROJ#843

At present, the fix is only in place for the C library.  Still need to
handle other cases of float -> int conversion.  (A check already in
place in the python library.)

legacy/C/geodesic.c

@@ -238,7 +238,7 @@ static void sincosdx(real x, real* sinx, real* cosx) {
   r = remquo(x, (real)(90), &q);
 #else
   r = fmod(x, (real)(360));
-  q = (int)(floor(r / 90 + (real)(0.5)));
+  q = r == r ? (int)(floor(r / 90 + (real)(0.5))) : 0;
   r -= 90 * q;
 #endif
   /* now abs(r) <= 45 */