substr() returns an empty string instead of false in 8.0

an empty string will pass through preg_match_all() without any harmful effects, so we don't need to check for it.

tests/phpstan/configs/phpstan-bugs.neon

@@ -35,11 +35,6 @@ parameters:
 			count: 1
 			path: ../../../src/plugin/ScriptPluginLoader.php
 
-		-
-			message: "#^Strict comparison using \\=\\=\\= between string and false will always evaluate to false\\.$#"
-			count: 1
-			path: ../../../src/utils/Utils.php
-
 		-
 			message: "#^Call to function is_resource\\(\\) with resource will always evaluate to true\\.$#"
 			count: 2