Improve exception for unexpected error

Author: rmaucher

java/org/apache/catalina/mapper/LocalStrings.properties

@@ -19,6 +19,7 @@ mapper.addHost.sameHost=Duplicate registration of the same host [{0}]. Ignored.
 mapper.addHost.success=Registered host [{0}]
 mapper.addHostAlias.sameHost=Duplicate registration of alias [{0}] for the same host [{1}]. Ignored.
 mapper.addHostAlias.success=Registered alias [{0}] for host [{1}]
+mapper.alreadyDone=Mapping was already done on this request on host [{0}]
 mapper.duplicateHost=Duplicate Host [{0}]. The name is already used by Host [{1}]. This Host will be ignored.
 mapper.duplicateHostAlias=Duplicate host Alias [{0}] in Host [{1}]. The name is already used by Host [{2}]. This Alias will be ignored.
 mapper.findContext.noContext=No context found [{0}]

java/org/apache/catalina/mapper/Mapper.java

@@ -710,7 +710,7 @@ private void internalMap(CharChunk host, CharChunk uri, String version, MappingD
             // skipped all mapping work in this case. That behaviour has a risk
             // of returning an inconsistent result.
             // I do not see a valid use case for it.
-            throw new AssertionError();
+            throw new IllegalStateException(sm.getString("mapper.alreadyDone", mappingData.host));
         }
 
         // Virtual host mapping