flip an if statement

src/board.rs

@@ -269,12 +269,13 @@ impl Board {
         if self.get(i, j).is_some() {
             return Err("position is occupied");
         }
+
         self.place_unchecked(i, j, piece);
-        if self.propegate_from(i, j) > 0 {
-            Ok(())
-        } else {
+        if self.propegate_from(i, j) == 0 {
             self.delete(i, j);
             Err("move would not propegate")
+        } else {
+            Ok(())
         }
     }