format-table: introduce table_isempty and use it where appropriate

src/shared/format-table.h

@@ -144,6 +144,12 @@ static inline TableCell* TABLE_HEADER_CELL(size_t i) {
 }
 
 size_t table_get_rows(Table *t);
+static inline bool table_isempty(Table *t) {
+        if (!t)
+                return true;
+
+        return table_get_rows(t) <= 1;
+}
 size_t table_get_columns(Table *t);
 
 size_t table_get_current_column(Table *t);

src/shared/pkcs11-util.c

@@ -1530,7 +1530,7 @@ int pkcs11_list_tokens(void) {
         if (r < 0 && r != -EAGAIN)
                 return r;
 
-        if (table_get_rows(t) <= 1) {
+        if (table_isempty(t)) {
                 log_info("No suitable PKCS#11 tokens found.");
                 return 0;
         }

src/shared/tpm2-util.c

@@ -5965,7 +5965,7 @@ int tpm2_list_devices(void) {
                 }
         }
 
-        if (table_get_rows(t) <= 1) {
+        if (table_isempty(t)) {
                 log_info("No suitable TPM2 devices found.");
                 return 0;
         }