Fix for multiple test failures on some platforms.

sql/sql_lex.cc:
  Added a debug assertion that the passed string is not empty.
sql/sql_show.cc:
  Do not quote empty string.

sql/sql_lex.cc

@@ -223,7 +223,7 @@ static int find_keyword(LEX *lex, uint len, bool function)
 
   SYNOPSIS
     is_keyword()
-    name      checked name
+    name      checked name (must not be empty)
     len       length of checked name
 
   RETURN VALUES
@@ -233,6 +233,7 @@ static int find_keyword(LEX *lex, uint len, bool function)
 
 bool is_keyword(const char *name, uint len)
 {
+  DBUG_ASSERT(len != 0);
   return get_hash_symbol(name,len,0)!=0;
 }
 

sql/sql_show.cc

@@ -713,7 +713,8 @@ append_identifier(THD *thd, String *packet, const char *name, uint length)
 
 int get_quote_char_for_identifier(THD *thd, const char *name, uint length)
 {
-  if (!is_keyword(name,length) &&
+  if (!length ||
+      !is_keyword(name,length) &&
       !require_quotes(name, length) &&
       !(thd->options & OPTION_QUOTE_SHOW_CREATE))
     return EOF;