[release/7.0-rc2] Handle a null szPname field (#75716)

* Handle a null szPname field

* Always clear the span to ensure we have a null terminator in case the string is short

* Use null conditional access

* Add call to test to test scenario

* Update src/libraries/System.Speech/tests/SynthesizeRecognizeTests.cs

Co-authored-by: Jeremy Koritzinsky <jkoritzinsky@gmail.com>
Co-authored-by: Jeremy Koritzinsky <jekoritz@microsoft.com>

Author: github-actions[bot]

src/libraries/Common/src/Interop/Windows/WinMm/Interop.waveOutGetDevCaps.cs

@@ -50,7 +50,9 @@ public Native(WAVEOUTCAPS managed)
                         wMid = managed.wMid;
                         wPid = managed.wPid;
                         vDriverVersion = managed.vDriverVersion;
-                        managed.szPname.CopyTo(MemoryMarshal.CreateSpan(ref szPname[0], szPnameLength));
+                        Span<char> szPnameSpan = MemoryMarshal.CreateSpan(ref szPname[0], szPnameLength);
+                        szPnameSpan.Clear();
+                        managed.szPname?.CopyTo(szPnameSpan);
                         dwFormats = managed.dwFormats;
                         wChannels = managed.wChannels;
                         wReserved1 = managed.wReserved1;