[d3d9] Fix and clarify Get/SetMapFlag interactions

src/d3d9/d3d9_common_buffer.h

@@ -128,9 +128,9 @@ namespace dxvk {
       return m_sliceHandle;
     }
 
-    DWORD GetMapFlags(DWORD Flags) { return m_mapFlags; }
+    DWORD GetMapFlags() const      { return m_mapFlags; }
 
-    DWORD SetMapFlags(DWORD Flags) { return std::exchange(m_mapFlags, Flags); }
+    DWORD SetMapFlags(DWORD Flags) { m_mapFlags = Flags; }
 
     const D3D9_BUFFER_DESC* Desc() const {
       return &m_desc;

src/d3d9/d3d9_device.cpp

@@ -4435,7 +4435,7 @@ namespace dxvk {
 
     *ppbData = reinterpret_cast<void*>(data);
 
-    DWORD oldFlags = pResource->GetMapFlags(Flags);
+    DWORD oldFlags = pResource->GetMapFlags();
 
     // We need to remove the READONLY flags from the map flags
     // if there was ever a non-readonly upload.
@@ -4484,9 +4484,11 @@ namespace dxvk {
     if (pResource->GetMapMode() != D3D9_COMMON_BUFFER_MAP_MODE_BUFFER)
       return D3D_OK;
 
-    if (pResource->GetMapFlags(0) & D3DLOCK_READONLY)
+    if (pResource->GetMapFlags() & D3DLOCK_READONLY)
       return D3D_OK;
 
+    pResource->SetMapFlags(0);
+
     if (pResource->Desc()->Pool != D3DPOOL_DEFAULT) {
       pResource->MarkNeedsUpload();
       return D3D_OK;