[win] Resolve the module only if there isn't one already

Summary:
This commit modifies the OnLoadModule method to resolve the module
unless we already have one

Change by Hui Huang to fix the failing LLDB tests on Windows

Reviewers: labath, asmith

Subscribers: abidh, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D58303

llvm-svn: 354172