clang analysis: garbage values

< src/cursor/cur_metadata.c:356:6: warning: The left operand of '==' is a garbage value

<         if (WT_KEY_IS_METADATA(&cursor->key))

<             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

< src/cursor/cur_metadata.c:158:3: note: expanded from macro 'WT_KEY_IS_METADATA'

<         (WT_STRING_MATCH(WT_METADATA_URI, (key)->data, (key)->size - 1) ||\

<          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

< ./src/include/misc.h:228:52: note: expanded from macro 'WT_STRING_MATCH'

<             strncmp(str, bytes, len) == 0 && (str)[(len)] == '\0')

<                                              ~~~~~~~~~~~~ ^