fix null pointer exception (#6093)

Signed-off-by: parneet-guraya <[email protected]>

Author: parneet-guraya

Diff for: app/src/main/java/fr/free/nrw/commons/wikidata/mwapi/MwQueryPage.kt

@@ -34,7 +34,7 @@ class MwQueryPage : BaseModel() {
 
     fun title(): String = title!!
 
-    fun categoryInfo(): CategoryInfo = categoryinfo!!
+    fun categoryInfo(): CategoryInfo? = categoryinfo
 
     fun index(): Int = index