fix(search2): Prevent StringIndexOutOfBoundsException in SuggestQuery

[andersju]

It can happen that the placeholder is missing, resulting in an exception. Noticed on QA with the query /find?_q=NOT+kategori%3A%28*%29&_limit=5&cursor=15&_sort=&_r=&_suggest=true:

2025-12-11T10:03:41,418 [qtp550147359-316] ERROR whelk.util.http.HttpTools - Internal server error: Range [0, -1) out of bounds for length 14
java.lang.StringIndexOutOfBoundsException: Range [0, -1) out of bounds for length 14
	at whelk.search2.SuggestQuery.lambda$getPartialCollectionView$0(SuggestQuery.java:68) ~[rest.jar:?]
	at whelk.search2.SuggestQuery.lambda$getPartialCollectionView$1(SuggestQuery.java:78) ~[rest.jar:?]
	at whelk.search2.SuggestQuery.getPartialCollectionView(SuggestQuery.java:81) ~[rest.jar:?]
	at whelk.search2.Query.collectResults(Query.java:111) ~[rest.jar:?]
	at whelk.rest.api.SearchUtils2.doSearch(SearchUtils2.java:41) ~[rest.jar:?]
	at whelk.rest.api.SiteSearch.findData(SiteSearch.java:138) ~[rest.jar:?]
	at whelk.rest.api.Crud.handleQuery(Crud.java:145) ~[rest.jar:?]
	at whelk.rest.api.Crud.doGet2(Crud.java:123) ~[rest.jar:?]
	at whelk.rest.api.Crud.doGet(Crud.java:103) ~[rest.jar:?]
...

[kwahlin]

LGTM! Let's merge this and fix the actual problem later.