[Bug 9594] New: Steam shows a blank white screen when attempting to purchase

http://bugs.winehq.org/show_bug.cgi?id=9594

Summary: Steam shows a blank white screen when attempting to
                    purchase
           Product: Wine
           Version: 0.9.44.
          Platform: PC
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: wine-tools
        AssignedTo: [e-mail]
        ReportedBy: [e-mail]

To reproduce:

Open Steam, select a game and click purchase. Web page window goes white but
remains responsive to other input (clicking "back", etc). New bug since 0.9.43

Regression testing identifies the patch which causes this as

mshtml: Return wine: URI for protocols handled by MSHTML.

SHA1 ID 718b771f2a57d0c762d24c6ef62f070eb3647e8a