MI Refactor CMIUtilSystemWindows::GetExecutablesPath()

[ki.stfu]

Summary

My understanding of the Windows API call GetLastError() is that it should only be checked when ::GetModuleFileName() returns 0 on error.
Otherwise GetExecutablesPath() could return an error despite nLen being valid if GetLastError() was inconsistent.
Patch updates function to only call GetOSLastError() when nLen == 0

Patch from [e-mail]

[ki.stfu]

lgtm. Should I commit it for you?

UPDATE:
btw, thx a lot! it annoyed me.

[EwanCrawford]

Yes, thanks again.

[ki.stfu]

Rebase against ToT

lldb/trunk/tools/lldb-mi/MIUtilSystemWindows.cpp

 // Throws:  None.
 //--
 bool
 CMIUtilSystemWindows::GetExecutablesPath(CMIUtilString &vrwFileNamePath) const
 {
     bool bOk = MIstatus::success;
     HMODULE hModule = ::GetModuleHandle(nullptr);
     char pPath[MAX_PATH];
-    const DWORD nLen = ::GetModuleFileName(hModule, &pPath[0], MAX_PATH);
-    const CMIUtilString strLastErr(GetOSLastError());
-    if ((nLen != 0) && (strLastErr == "Unknown OS error"))
-        vrwFileNamePath = &pPath[0];
-    else
+    if (!::GetModuleFileName(hModule, &pPath[0], MAX_PATH))
     {
         bOk = MIstatus::failure;
-        vrwFileNamePath = strLastErr;
+        vrwFileNamePath = GetOSLastError();
     }
+    else
+        vrwFileNamePath = &pPath[0];
 
     return bOk;
 }
 
 //++ ------------------------------------------------------------------------------------
 // Details: Retrieves the fully qualified path for the Log file for this application.
 //          If the function fails the string is filled with the error message.
 // Type:    Method.