ast-build: fix leak in error path

Signed-off-by: Ran Benita <ran234@gmail.com>

src/xkbcomp/ast-build.c

@@ -304,6 +304,7 @@ VarDef *
 BoolVarCreate(xkb_atom_t ident, bool set)
 {
     ExprDef *name, *value;
+    VarDef *def;
     if (!(name = ExprCreateIdent(ident))) {
         return NULL;
     }
@@ -311,7 +312,12 @@ BoolVarCreate(xkb_atom_t ident, bool set)
         FreeStmt((ParseCommon *) name);
         return NULL;
     }
-    return VarCreate(name, value);
+    if (!(def = VarCreate(name, value))) {
+        FreeStmt((ParseCommon *) name);
+        FreeStmt((ParseCommon *) value);
+        return NULL;
+    }
+    return def;
 }
 
 InterpDef *