[SHIRO-742]fix throw exception when request uri is /

[tomsun28]

this bug due to my pr SHIRO-682 fix the potential threat when use "uri = uri + '/' " to bypassed shiro in 1.5, sorry

as the @JaynLau comment
under is @JaynLau report

Can not get the NamedFilterList when request uri is "/".

java.lang.IllegalArgumentException: There is no configured chain under the name/key [].
	at org.apache.shiro.web.filter.mgt.DefaultFilterChainManager.proxy(DefaultFilterChainManager.java:322) ~[shiro-web-1.5.0.jar:1.5.0]
	at org.apache.shiro.web.filter.mgt.PathMatchingFilterChainResolver.getChain(PathMatchingFilterChainResolver.java:126) ~[shiro-web-1.5.0.jar:1.5.0]
	at org.apache.shiro.web.servlet.AbstractShiroFilter.getExecutionChain(AbstractShiroFilter.java:415) ~[shiro-web-1.5.0.jar:1.5.0]
	at org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:448) ~[shiro-web-1.5.0.jar:1.5.0]
	at org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365) ~[shiro-web-1.5.0.jar:1.5.0]
	at org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90) ~[shiro-core-1.5.0.jar:1.5.0]
	at org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83) ~[shiro-core-1.5.0.jar:1.5.0]
	at org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:387) ~[shiro-core-1.5.0.jar:1.5.0]
	at org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:362) ~[shiro-web-1.5.0.jar:1.5.0]

The value of pathPattern is changed from "/" to "" , matching path definition / = user failed.
Because chainName is "/", not "".

this pr's solution is bypass substring when the request uri and pathPattern is /
please let me konw if any other better solution,
thanks @JaynLau ^~^

[fpapon]

@tomsun28 thanks for the PR. We are releasing the 1.5.1 and we will merge this just after.

[fpapon]

LGTM
thanks!

[adessaigne]

Hello.
First, thank you very much for this fix.
I have a newbie question: would it be possible to include this commit in 1.5.1 release? I have to admit I'm not yet familiar with the release process. Thank you very much!

[coheigea]

Yes, it will be in the 1.5.1 release.