AK: Don't compare past '\0' in StringView::operator==(const char*)

We kept scanning the needle string even after hitting a null terminator
and that's clearly not right.

Found by oss-fuzz:
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=31338
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=31351

AK/StringView.h

@@ -147,6 +147,8 @@ public:
         // NOTE: `m_characters` is not guaranteed to be null-terminated, but `cstring` is.
         const char* cp = cstring;
         for (size_t i = 0; i < m_length; ++i) {
+            if (!*cp)
+                return false;
             if (m_characters[i] != *(cp++))
                 return false;
         }