Fix crash when searching non-table documentation

src/fennel-ls/language.fnl

@@ -68,7 +68,8 @@ find the definition `10`, but if `opts.stop-early?` is set, it would find
   (doto opts (tset :searched-through-require true))
   (if (= 0 (length stack))
     document
-    (. document.fields (. stack (length stack)))
+    (and document.fields
+         (. document.fields (. stack (length stack))))
     (search-document self (. document.fields (table.remove stack)) stack opts)))
 
 (λ search-val [self file ast stack opts]

test/hover.fnl

@@ -118,6 +118,7 @@ new message handler `msgh`.")
 (fn test-crash []
   (check "|(local x {:foo \"hello\"}) x.foo" nil)
   (check "|\n(local x {:foo \"hello\"}) x.foo" nil)
+  (check "print.my-cool-real-field|" nil)
   nil)
 
 (fn test-multival []