Fix potential leak in bssl::Array::Shrink.

We don't currently use this type anywhere with a nontrivial destructor,
so this doesn't matter right now. But handle this correctly in case we
ever do. (One of these days, we should sort out using the STL and Abseil
in here...)

Change-Id: I6a198ccf87f953cedcdbe658fa508a3b79d47305
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/42825
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>

ssl/internal.h

@@ -345,6 +345,9 @@ class Array {
     if (new_size > size_) {
       abort();
     }
+    for (size_t i = new_size; i < size_; i++) {
+      data_[i].~T();
+    }
     size_ = new_size;
   }