Fix: oclass was not read properly from swapchest file

... after the change earlier to silence a compiler warning. Reading a
character from the file is incorrect since we write oclass as an
integer, so it would probably attempt to read the first digit of that
integer as a character and set the resulting object's class to an
invalid value. Who knows what undefined behavior would have resulted.

Instead, read the oclass from the file into an int variable, then cast
that to char for setting the actual object's class.

src/files.c

@@ -4924,8 +4924,12 @@ short *rcode;
             continue;
         if (sscanf(buf, "spe=%hhd", &(o->spe)) == 1)
             continue;
-        if (sscanf(buf, "oclass=%c", &(o->oclass)) == 1)
+        if (sscanf(buf, "oclass=%d", &tmp_bitfield) == 1) {
+            /* oclass isn't a bitfield but read it as an int to silence a
+             * compiler warning for reading an int directly into a char */
+            o->oclass = (char) tmp_bitfield;
             continue;
+        }
         if (sscanf(buf, "cursed=%d", &tmp_bitfield) == 1) {
             o->cursed = tmp_bitfield;
             continue;