NULL out registers on re-OSR.

If we previously ran the OSR'd code for this frame, then we don't need
to resize work/env. However, they were unused while the deopt code was
being run, and so may contain outdated pointers that will upset the
GC if it comes across them. Fix this by making sure that space is
cleared out.

src/spesh/osr.c

@@ -52,6 +52,11 @@ void perform_osr(MVMThreadContext *tc, MVMSpeshCandidate *specialized) {
         MVM_string_utf8_encode_C_string(tc, tc->cur_frame->static_info->body.cuuid));
 #endif
     }
+    else if (specialized->work_size > tc->cur_frame->static_info->body.work_size) {
+        size_t keep_bytes = tc->cur_frame->static_info->body.num_locals * sizeof(MVMRegister);
+        size_t to_null = specialized->work_size - keep_bytes;
+        memset((char *)tc->cur_frame->work + keep_bytes, 0, to_null);
+    }
 
     /* Resize environment if needed. */
     if (specialized->num_lexicals > tc->cur_frame->static_info->body.num_lexicals) {
@@ -71,6 +76,11 @@ void perform_osr(MVMThreadContext *tc, MVMSpeshCandidate *specialized) {
         MVM_string_utf8_encode_C_string(tc, tc->cur_frame->static_info->body.cuuid));
 #endif
     }
+    else if (specialized->env_size > tc->cur_frame->static_info->body.env_size) {
+        size_t keep_bytes = tc->cur_frame->static_info->body.num_lexicals * sizeof(MVMRegister);
+        size_t to_null = specialized->env_size - keep_bytes;
+        memset((char *)tc->cur_frame->env + keep_bytes, 0, to_null);
+    }
 
     /* Set up frame to point to specialized code. */
     tc->cur_frame->effective_bytecode    = specialized->bytecode;