Fix expr JITed ordbaseat and getcpbyname returning 4294967295 instead…

… of -1

I missed ordbaseat in the expr JIT in commit 3a62bdf
The same issue existed with getcpbyname: it returns an MVMGrapheme32 which is a
32 bit signed integer. However we treated it as a 64 bit integer without proper
sign extension, which turned a -1 into 4294967295.
Fix by sign extend the result to a full 64 bit signed integer.

src/jit/core_templates.expr

@@ -589,10 +589,11 @@
       (carg $2 ptr)) ptr_sz))
 
 (template: getcpbyname
-  (call (^func &MVM_unicode_lookup_by_name)
-    (arglist
-      (carg (tc) ptr)
-      (carg $1 ptr)) int_sz))
+  (scast
+    (call (^func &MVM_unicode_lookup_by_name)
+      (arglist
+        (carg (tc) ptr)
+        (carg $1 ptr)) int_sz) int_sz 4))
 
 (template: unipropcode
   (call (^func &MVM_unicode_name_to_property_code)
@@ -2341,11 +2342,12 @@
       (carg $3 int)) int_sz))
 
 (template: ordbaseat
-  (call (^func &MVM_string_ord_basechar_at)
-    (arglist
-      (carg (tc) ptr)
-      (carg $1 ptr)
-      (carg $2 int)) int_sz))
+  (scast
+    (call (^func &MVM_string_ord_basechar_at)
+      (arglist
+        (carg (tc) ptr)
+        (carg $1 ptr)
+        (carg $2 int)) int_sz) int_sz 4))
 
 (template: isrwcont
   (if