Fix crash in set registers in PPC gdb-stub, by Jason Wessel.

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@3079 c046a42c-6fe2-441c-8c8c-71466251a162

target-ppc/helper.c

@@ -1493,11 +1493,13 @@ void do_store_msr (CPUPPCState *env, target_ulong value)
         break;
     }
     if (enter_pm) {
+        if (likely(!env->halted)) {
             /* power save: exit cpu loop */
             env->halted = 1;
             env->exception_index = EXCP_HLT;
             cpu_loop_exit();
         }
+    }
 }
 
 #if defined(TARGET_PPC64)