BLI_string: add BLI_strchr_or_end

Returning the pointer to the null byte when the character isn't found
is useful when handling null terminated strings that contain newlines.

This means the return value is never null and the line span always ends
at the resulting value.

source/blender/blenlib/BLI_string.h

@@ -114,6 +114,16 @@ size_t BLI_strcpy_rlen(char *__restrict dst, const char *__restrict src) ATTR_WA
 char *BLI_strncat(char *__restrict dst, const char *__restrict src, size_t dst_maxncpy)
     ATTR_NONNULL(1, 2);
 
+/**
+ * A version of `strchr` that returns the end of the string (point to `\0`)
+ * if the character is not found.
+ *
+ * Useful for stepping over newlines up until the last line.
+ */
+const char *BLI_strchr_or_end(const char *str,
+                              char ch) ATTR_WARN_UNUSED_RESULT ATTR_RETURNS_NONNULL
+    ATTR_NONNULL(1);
+
 /**
  * Return the range of the quoted string (excluding quotes) `str` after `prefix`.
  *

source/blender/blenlib/intern/string.c

@@ -988,6 +988,21 @@ size_t BLI_strnlen(const char *s, const size_t maxlen)
 
 /** \} */
 
+/* -------------------------------------------------------------------- */
+/** \name String Scanning
+ * \{ */
+
+const char *BLI_strchr_or_end(const char *str, const char ch)
+{
+  const char *p = str;
+  while (!ELEM(*p, ch, '\0')) {
+    p++;
+  }
+  return p;
+}
+
+/** \} */
+
 /* -------------------------------------------------------------------- */
 /** \name String Case Conversion
  * \{ */