[db_init] Set admint.value to VARCHAR(255)

Only a cosmetic change to avoid future confusion. sqlite3 ignores the
number of chars given to VARCHAR (see https://sqlite.org/faq.html#q9 ),
a db upgrade is therefor not necessary.

src/db_init.c

@@ -28,7 +28,7 @@
 #define T_ADMIN						\
   "CREATE TABLE IF NOT EXISTS admin("			\
   "   key   VARCHAR(32) PRIMARY KEY NOT NULL,"		\
-  "   value VARCHAR(32) NOT NULL"			\
+  "   value VARCHAR(255) NOT NULL"			\
   ");"
 
 #define T_FILES						\