tidy: Ignore false positive memory leak warning.

Clang-tidy complains that the sub_read_file function leaks memory at
the return statement at the end of the function, saying that the
memory of the 'sub' variable is leaked.  The pointer is always set as
a result of a function call to parse something, and it typically set
to point to the memory provided by the second argument.  The only
other possible values are nullptr or an error code.  Since this
pointer never owns any memory, there can't be a memory leak.

https://clang.llvm.org/extra/clang-tidy/checks/clang-analyzer-unix.Malloc.html

mythtv/libs/libmythtv/xine_demux_sputext.cpp

@@ -1120,6 +1120,8 @@ subtitle_t *sub_read_file (demux_sputext_t *demuxstr) {
   int n_max;
   int timeout;
   subtitle_t *first;
+  // These functions all return either 1) nullptr, 2) (subtitle_t*)ERR,
+  // or 3) a pointer to the dest parameter.
   subtitle_t * (*func[])(demux_sputext_t *demuxstr,subtitle_t *dest)=
   {
     sub_read_line_microdvd,
@@ -1164,8 +1166,6 @@ subtitle_t *sub_read_file (demux_sputext_t *demuxstr) {
   else timeout *= 10;
 
   while(true) {
-    subtitle_t *sub;
-
     if(demuxstr->num>=n_max){
       n_max+=16;
       auto *new_first=(subtitle_t *)realloc(first,n_max*sizeof(subtitle_t));
@@ -1176,8 +1176,7 @@ subtitle_t *sub_read_file (demux_sputext_t *demuxstr) {
       first = new_first;
     }
 
-    sub = func[demuxstr->format] (demuxstr, &first[demuxstr->num]);
-
+    subtitle_t *sub = func[demuxstr->format] (demuxstr, &first[demuxstr->num]);
     if (!sub) {
       break;   /* EOF */
     }
@@ -1223,5 +1222,7 @@ subtitle_t *sub_read_file (demux_sputext_t *demuxstr) {
   }
 #endif
 
+  // No memory leak of 'sub' here.  'Sub' always points to an element in 'first'.
+  // NOLINT(clang-analyzer-unix.Malloc)
   return first;
 }