fix #2994 by fixing block aborts() definition

lib/compress.js

@@ -3074,8 +3074,12 @@ merge(Compressor.prototype, {
         def(AST_Statement, return_null);
         def(AST_Jump, return_this);
         function block_aborts(){
-            var n = this.body.length;
-            return n > 0 && aborts(this.body[n - 1]);
+            for (var i = 0; i < this.body.length; i++) {
+                if (aborts(this.body[i])) {
+                    return this.body[i];
+                }
+            }
+            return null;
         };
         def(AST_Import, function(){ return null; });
         def(AST_BlockStatement, block_aborts);

test/compress/conditionals.js

@@ -1204,6 +1204,45 @@ issue_2560: {
     ]
 }
 
+issue_2994: {
+    options = {
+        conditionals: true,
+        if_return: true
+    }
+    input: {
+        function f() {
+            if (condition1) {
+                if (condition2) {
+                    return aValue;
+                } else {
+                    const variable1 = 'something';
+                    if (condition3) {
+                        const variable2 = 'else';
+                        return anotherValue;
+                    } else {
+                        return undefined;
+                    }
+                }
+            }
+        }
+    }
+    expect: {
+        function f() {
+            if (condition1) {
+                if (condition2) return aValue;
+                {
+                    const variable1 = 'something';
+                    if (condition3) {
+                        const variable2 = 'else';
+                        return anotherValue;
+                    }
+                    return;
+                }
+            }
+        }
+    }
+}
+
 hoist_decl: {
     options = {
         conditionals: true,