Fix PHP Notice in user_cache_row()

If the function receives an invalid user ID, it will issue an Undefined
offset notice, as it does not check for actual existence of the ID in
the users' cache after calling user_cache_array_rows().

PHPDoc does state that a valid user ID is expected, but since the
function includes error handling code, it makes sense to account for
this case, unlikely as it may be.

Fixes #25850

core/user_api.php

@@ -83,23 +83,21 @@ function user_cache_row( $p_user_id, $p_trigger_errors = true ) {
 
 	if( !isset( $g_cache_user[$c_user_id] ) ) {
 		user_cache_array_rows( array( $c_user_id ) );
-	}
 
-	$t_user_row = $g_cache_user[$c_user_id];
+		if( !isset( $g_cache_user[$c_user_id] ) ) {
+			if( $p_trigger_errors ) {
+				throw new ClientException(
+					sprintf( "User id '%d' not found.", (integer)$p_user_id ),
+					ERROR_USER_BY_ID_NOT_FOUND,
+					array( (integer)$p_user_id )
+				);
+			}
 
-	if( !$t_user_row ) {
-		if( $p_trigger_errors ) {
-			throw new ClientException(
-				sprintf( "User id '%d' not found.", (integer)$p_user_id ),
-				ERROR_USER_BY_ID_NOT_FOUND,
-				array( (integer)$p_user_id )
-			);
+			return false;
 		}
-
-		return false;
 	}
 
-	return $t_user_row;
+	return $g_cache_user[$c_user_id];
 }
 
 /**
@@ -131,14 +129,16 @@ function user_cache_array_rows( array $p_user_id_array ) {
 	$t_query = 'SELECT * FROM {user} WHERE id IN (' . implode( ',', $t_sql_in_params ) . ')';
 	$t_result = db_query( $t_query, $t_params );
 
-	while( $t_row = db_fetch_array( $t_result ) ) {
-		$c_user_id = (int)$t_row['id'];
-		$g_cache_user[$c_user_id] = $t_row;
-		unset( $c_user_id_array[$c_user_id] );
-	}
-	# set the remaining ids to false as not-found
-	foreach( $c_user_id_array as $t_id ) {
-		$g_cache_user[$t_id] = false;
+	if( $t_result !== false ) {
+		while( $t_row = db_fetch_array( $t_result ) ) {
+			$c_user_id = (int)$t_row['id'];
+			$g_cache_user[$c_user_id] = $t_row;
+			unset( $c_user_id_array[$c_user_id] );
+		}
+		# set the remaining ids to false as not-found
+		foreach( $c_user_id_array as $t_id ) {
+			$g_cache_user[$t_id] = false;
+		}
 	}
 }
 
@@ -1790,4 +1790,4 @@ function user_has_more_than_one_project( $p_user_id ) {
 		}
 	}
 	return true;
-}
+}