mf: Do not touch clock state when setting rate.

dlls/mf/session.c

@@ -2978,7 +2978,8 @@ static HRESULT clock_change_state(struct presentation_clock *clock, enum clock_c
         return hr;
 
     old_state = clock->state;
-    clock->state = states[command];
+    if (command != CLOCK_CMD_SET_RATE)
+        clock->state = states[command];
 
     /* Dump all pending timer requests immediately on start; otherwise try to cancel scheduled items when
        transitioning from running state. */

dlls/mf/tests/mf.c

@@ -1797,6 +1797,10 @@ static void test_presentation_clock(void)
     hr = IMFRateControl_SetRate(rate_control, TRUE, -1.0f);
     ok(hr == MF_E_THINNING_UNSUPPORTED, "Unexpected hr %#x.\n", hr);
 
+    hr = IMFPresentationClock_GetState(clock, 0, &state);
+    ok(hr == S_OK, "Failed to get clock state, hr %#x.\n", hr);
+    ok(state == MFCLOCK_STATE_RUNNING, "Unexpected state %d.\n", state);
+
     hr = IMFRateControl_GetRate(rate_control, &thin, &rate);
     ok(hr == S_OK, "Failed to get clock rate, hr %#x.\n", hr);
     ok(rate == 0.5f, "Unexpected rate.\n");