Use system library function to byte swap VCT short channel name.

Qt 6.1 added overloads to the QChar constructor that catch an int or
uint argument, and use an assert to validate that the passed value
fits in 16 bits. The current implementation calls the uint version of
the constructor, and will crash if it is ever passed a number outside
of the range 0-65535, which means passing the number -1 will cause a
crash.

Converting the exiting manual byte swap to use be16toh() serves two
purposes. First it guarantees that the result is a uint16_t and
therefore can't trigger the assert. Second, it should result in
correct values if this code is ever compiled on a big-endian system.

mythtv/libs/libmythtv/mpeg/atsctables.h

@@ -4,6 +4,14 @@
 #define ATSC_TABLES_H
 
 #include <cstdint>  // uint32_t
+#if HAVE_SYS_ENDIAN_H
+#include <sys/endian.h>
+#elif !CONFIG_DARWIN
+#include <endian.h>
+#else
+#include <libkern/OSByteOrder.h>
+#define be16toh(x) OSSwapBigToHostInt16(x)
+#endif
 #include <QString>
 
 #include "atscdescriptors.h"
@@ -231,7 +239,7 @@ class MTV_PUBLIC VirtualChannelTable : public PSIPTable
         const auto* ustr = reinterpret_cast<const unsigned short*>(m_ptrs[i]);
         for (int j=0; j<7; j++)
         {
-            QChar c((ustr[j]<<8) | (ustr[j]>>8));
+            QChar c(be16toh(ustr[j]));
             if (c != QChar('\0')) str.append(c);
         }
         return str.simplified();