Fix not operator

(cherry picked from commit 00c7d3a157d8d859ede501d71282e82fba40e37b)

worldedit-core/src/main/java/com/sk89q/worldedit/internal/expression/invoke/ExpressionHandles.java

@@ -237,7 +237,7 @@ class ExpressionHandles {
     }
 
     private static boolean doubleToBool(double bool) {
-        return bool > 0;
+        return bool != 0;
     }
 
     static double boolToDouble(boolean bool) {

worldedit-core/src/test/java/com/sk89q/worldedit/internal/expression/ExpressionTest.java

@@ -92,6 +92,15 @@ class ExpressionTest extends BaseExpressionTest {
         checkTestCase("a=0; b=--a; a+b", -2);
     }
 
+    @Test
+    void testNot() {
+        checkTestCase("!0", 1);
+        checkTestCase("!1", 0);
+        checkTestCase("!2", 0);
+        checkTestCase("!-1", 0);
+        checkTestCase("!-2", 0);
+    }
+
     @Test
     public void testErrors() {
         // test lexer errors