Update sp_BlitzCache.sql

Not sure this can happen either, but this also looks harmless, so taking it.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: BrentOzar

sp_BlitzCache.sql

@@ -5115,7 +5115,7 @@ SET
     b.Warnings = 'We couldn''t find a plan for this query. More info on possible reasons: https://www.brentozar.com/go/noplans'
 FROM ##BlitzCacheProcs AS b
 WHERE b.QueryPlan IS NULL
-AND   b.Warnings IS NULL
+AND   (b.Warnings IS NULL OR b.Warnings = '')
 AND   b.SPID = @@SPID
 OPTION (RECOMPILE);