tidy: Silence a couple of misleading "infinite loop" warnings.

The clang-tidy "infinite loop" checker pointed out a couple of places
that look like infinite loops, because the loop variable isn't updated
anywhere inside of the loop.  All of these are written in the form:

    while ( x=fn() )
        {...}

What clang-tidy doesn't see is that inside the function is an iterator
that will eventually return 0 and cause the loop to exit.  Tell
clang-tidy to ignore these loops in the future.

https://clang.llvm.org/extra/clang-tidy/checks/bugprone-infinite-loop.html

mythtv/libs/libmyth/audio/audiooutputalsa.cpp

@@ -361,6 +361,7 @@ AudioOutputSettings* AudioOutputALSA::GetOutputSettings(bool passthrough)
              "(using plugin?)");
     }
 
+    // NOLINTNEXTLINE(bugprone-infinite-loop)
     while (int rate = settings->GetNextRate())
         if(snd_pcm_hw_params_test_rate(m_pcm_handle, params, rate, 0) >= 0)
             settings->AddSupportedRate(rate);

mythtv/libs/libmyth/audio/audiooutputnull.cpp

@@ -55,11 +55,13 @@ AudioOutputSettings* AudioOutputNULL::GetOutputSettings(bool /*digital*/)
     // Pretend that we support everything
     AudioOutputSettings *settings = new AudioOutputSettings();
 
+    // NOLINTNEXTLINE(bugprone-infinite-loop)
     while (int rate = settings->GetNextRate())
     {
         settings->AddSupportedRate(rate);
     }
 
+    // NOLINTNEXTLINE(bugprone-infinite-loop)
     while (AudioFormat fmt = settings->GetNextFormat())
     {
         settings->AddSupportedFormat(fmt);

mythtv/libs/libmyth/audio/audiooutputoss.cpp

@@ -50,6 +50,7 @@ AudioOutputSettings* AudioOutputOSS::GetOutputSettings(bool /*digital*/)
         return nullptr;
     }
 
+    // NOLINTNEXTLINE(bugprone-infinite-loop)
     while (int rate = settings->GetNextRate())
     {
         int rate2 = rate;