make sure classes don't have their surrounding blocks removed too

lib/compress.js

@@ -3118,7 +3118,8 @@ merge(Compressor.prototype, {
     function can_be_extracted_from_if_block(node) {
         return !(
             node instanceof AST_Const ||
-            node instanceof AST_Let
+            node instanceof AST_Let ||
+            node instanceof AST_Class
         );
     }
 

test/compress/blocks.js

@@ -200,6 +200,11 @@ issue_2946_else_const: {
         } else {
             let w = 48;
         }
+        if (3) {
+            class X {}
+        } else {
+            class Y {}
+        }
     }
     expect: {
         if (1) {
@@ -212,5 +217,10 @@ issue_2946_else_const: {
         } else {
             let w = 48;
         }
+        if (3) {
+            class X {}
+        } else {
+            class Y {}
+        }
     }
 }