[d3d11] Reset implicit flush timer only when actually flushing

In some situations, calling Flush without any commands that
could be flushed would unnecessarily prevent the implicit
flush heuristic from kicking in properly.

src/d3d11/d3d11_context_imm.cpp

@@ -103,11 +103,10 @@ namespace dxvk {
       
       FlushCsChunk();
       
-    }
+      // Reset flush timer used for implicit flushes
-
-    // Reset optimization info
-    m_csIsBusy  = false;
       m_lastFlush = std::chrono::high_resolution_clock::now();
+      m_csIsBusy  = false;
+    }
   }