Explicitely return value 0 if we return without error

Explicitely return value 0 if we return without error
from setclasspath.bat. Otherwise errorlevel in catalina.bat
is not reset.

catalina.bat checks for non-zero errorlevel after
the call to setclasspath.bat and then fails silently,
because it assumes setclasspath.bat to log any error.

If there is an error above the call to setclasspath.bat,
catalina.bat fails without any message.

Since there is only very basic logic above the call
to setclasspath.bat, let us reset errorlevel to ignore errors.

Example: any "set myvar=" for an undefined variable myvar
sets errorlevel to 1, although it is a correct statement,
setting the variable to an empty value.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@793669 13f79535-47bb-0310-9956-ffa450edef68