smbios: Fix table when no string is present

When no string is present in a table, next_ptr points to the same
location as eos. When calculating the string table length, we would only
reserve one \0. By spec a SMBIOS table has to end with two \0\0 when no
strings a present.

Signed-off-by: Matthias Brugger <mbrugger@suse.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/lib/smbios.c b/lib/smbios.c
index 11b7611..0ae8578 100644
--- a/lib/smbios.c
+++ b/lib/smbios.c
@@ -312,6 +312,10 @@
  */
 static int smbios_string_table_len(const struct smbios_ctx *ctx)
 {
+	/* In case no string is defined we have to return two \0 */
+	if (ctx->next_ptr == ctx->eos)
+		return 2;
+
 	/* Allow for the final \0 after all strings */
 	return (ctx->next_ptr + 1) - ctx->eos;
 }