Fix: Draugr trying to read a spellbook and the spellbook is destroyed while reading it.

Author: k21971

doc/evilhack-changelog.md

@@ -3447,4 +3447,6 @@ The following changes to date are:
 - Draugr can revive
 - Fix: if burning hands or shocking grasp is active, don't activate
   whilst using thievery skill
+- Fix: Draugr trying to read a spellbook and the spellbook is
+  destroyed while reading it
 

src/spell.c

@@ -346,10 +346,18 @@ learn(VOID_ARGS)
     boolean costly = TRUE;
     struct obj *book = context.spbook.book;
 
+    if (!book) {
+        context.spbook.delay = 0;
+        context.spbook.o_id = 0;
+        return 0;
+    }
+
     /* JDS: lenses give 50% faster reading; 33% smaller read time */
     if (context.spbook.delay && ublindf && ublindf->otyp == LENSES && rn2(2))
         context.spbook.delay++;
-    if (Confusion || (Race_if(PM_DRAUGR) && book->otyp != SPE_BOOK_OF_THE_DEAD)) { /* became confused while learning */
+    if (Confusion
+        || (Race_if(PM_DRAUGR) && book
+            && book->otyp != SPE_BOOK_OF_THE_DEAD)) { /* became confused while learning */
         (void) confused_book(book);
         context.spbook.book = 0; /* no longer studying */
         context.spbook.o_id = 0;