Start implementing jdb "locals".

This lets us show the names and types of the locals, but all the values
will show up as 0/null. We're going to have to walk the whole stack and
take callee-save frames into account to do that right.

Change-Id: Ic6e115513b6e65ae7ed4b7274e70bc514e83190a
diff --git a/src/dex_file.h b/src/dex_file.h
index 8e07dde..92aa794 100644
--- a/src/dex_file.h
+++ b/src/dex_file.h
@@ -577,8 +577,8 @@
                            LocalInfo* local_in_reg, DexDebugNewLocalCb local_cb) const {
     if (local_cb != NULL && local_in_reg[reg].is_live_) {
       local_cb(cnxt, reg, local_in_reg[reg].start_address_, end_address,
-               local_in_reg[reg].name_, local_in_reg[reg].descriptor_,
-               local_in_reg[reg].signature_);
+          local_in_reg[reg].name_, local_in_reg[reg].descriptor_,
+          local_in_reg[reg].signature_ != NULL ? local_in_reg[reg].signature_ : "");
     }
   }