Refactor mb_substr_count()

Promote empty needle warning to ValueError
Convert if branch into an assertion as if mbfl_substr_count fails this now implies a bug
Thus mb_substr_count() can only return int now, fix stubs accordingly

1 files changed, 1 insertions, 1 deletions

diff --git a/ext/mbstring/mbstring.stub.php b/ext/mbstring/mbstring.stub.php
index aa2c7dc0e4..dfc920eb96 100644
--- a/ext/mbstring/mbstring.stub.php
+++ b/ext/mbstring/mbstring.stub.php
@@ -39,7 +39,7 @@ function mb_stristr(string $haystack, string $needle, bool $part = false, string
 
 function mb_strrichr(string $haystack, string $needle, bool $part = false, string $encoding = UNKNOWN): string|false {}
 
-function mb_substr_count(string $haystack, string $needle, string $encoding = UNKNOWN): int|false {}
+function mb_substr_count(string $haystack, string $needle, string $encoding = UNKNOWN): int {}
 
 function mb_substr(string $str, int $start, ?int $length = null, string $encoding = UNKNOWN): string|false {}