Reply with error on negative geo radius.

Thanks to @tidwall for reporting.
Close #3194.

src/geo.c

@@ -157,7 +157,10 @@ double extractDistanceOrReply(client *c, robj **argv,
     }
 
     double to_meters = extractUnitOrReply(c,argv[1]);
-    if (to_meters < 0) return -1;
+    if (to_meters < 0) {
+        addReplyError(c,"radius cannot be negative");
+        return -1;
+    }
 
     if (conversion) *conversion = to_meters;
     return distance * to_meters;