Increment self.len in specialized ZipImpl to avoid underflow in size_hint

Author: SkiFire13

library/core/src/iter/adapters/zip.rs

@@ -200,6 +200,7 @@ where
         } else if A::MAY_HAVE_SIDE_EFFECT && self.index < self.a.size() {
             let i = self.index;
             self.index += 1;
+            self.len += 1;
             // match the base implementation's potential side effects
             // SAFETY: we just checked that `i` < `self.a.len()`
             unsafe {