fix(PVS V507): false positive

https://pvs-studio.com/en/docs/warnings/v507/

"Pointer to local array 'sourcing_name_buf' is stored outside the scope
of this array. Such a pointer will become invalid."

False positive: `sourcing_name = save_sourcing_name` before returning
from this scope.

src/nvim/ex_cmds2.c

@@ -1950,7 +1950,7 @@ static int source_using_linegetter(void *cookie, LineGetter fgetline, const char
     snprintf((char *)sourcing_name_buf, sizeof(sourcing_name_buf),
              "%s called at %s:%" PRIdLINENR, traceback_name, save_sourcing_name,
              save_sourcing_lnum);
-    sourcing_name = sourcing_name_buf;
+    sourcing_name = sourcing_name_buf;  // -V507 reassigned below, before return.
   }
   sourcing_lnum = 0;
 

src/nvim/memory.c

@@ -170,6 +170,8 @@ void *xrealloc(void *ptr, size_t size)
 
 /// xmalloc() wrapper that allocates size + 1 bytes and zeroes the last byte
 ///
+/// Commonly used to allocate strings, e.g. `char *s = xmallocz(len)`.
+///
 /// @see {xmalloc}
 /// @param size
 /// @return pointer to allocated space. Never NULL