Fix running with PERL6LIB on JVM

Apparently, you cannot nqp::getattr into a native int on the JVM,
even if the attribute in question *is* a native int.

src/core/Str.pm

@@ -828,10 +828,20 @@ my class Str does Stringy { # declared in BOOTSTRAP
             nqp::setelems($result,$elems + 1);
             while nqp::islt_i($i,$elems) {
                 $match := nqp::decont(nqp::atpos($matches,$i));
+#?if jvm
+                $found  = $match.from;
+#?endif
+#?if !jvm
                 $found  = nqp::getattr($match,Match,'$!from');
+#?endif
                 nqp::bindpos($result,$i,
                   nqp::substr($str,$pos,nqp::sub_i($found,$pos)));
+#?if jvm
+                $pos = $match.to;
+#?endif
+#?if !jvm
                 $pos = nqp::getattr($match,Match,'$!to');
+#?endif
                 $i   = nqp::add_i($i,1);
             }
             nqp::bindpos($result,$i,nqp::substr($str,$pos));