Fix the issue #2302, bug when namespace starts with a space.

[Fudeveloper]

When we use the method MapperBuilderAssistant#getStatementResultMaps, the name is trimmed . But in the method Configuration#AddResultMap, there is no trim operation. These asymmetrical operations will lead to this happening.

Perhaps, we can throw an error directly in the build phase when Namespace begins with a space. Just like this in method XMLMapperBuilder#configurationElement.

private void configurationElement(XNode context) {
    try {
      String namespace = context.getStringAttribute("namespace");
      if (namespace == null || namespace.isEmpty()) {
        throw new BuilderException("Mapper's namespace cannot be empty");
      }
      // like this
      if (namespace.startsWith(" ")) {
        throw new BuilderException("Mapper's namespace cannot start with whitespace.");
      }
     
        ...
    } catch (Exception e) {
      throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e);
    }
  }

[coveralls]

Coverage remained the same at 87.248% when pulling 0349cec on Fudeveloper:issue#2302 into 0cf1efb on mybatis:master.

[harawata]

I should've closed this along with #2302 .