Improve field query and fix mariadb's pickiness with parens

If no query is given, don't search with `like '%'`. MariaDB doesn't
want parens around columns in the GROUP BY clause.

modules/store/src/test/scala/docspell/store/queries/QueryWildcardTest.scala

@@ -18,4 +18,9 @@ object QueryWildcardTest extends SimpleTestSuite {
     assertEquals("%name%", QueryWildcard("*name*"))
     assertEquals("%some other name%", QueryWildcard("*some other name*"))
   }
+
+  test("do not use multiple wildcards") {
+    assertEquals("%", QueryWildcard("**"))
+    assertEquals("%*%", QueryWildcard("***"))
+  }
 }