Merge #89: header: Delete default Minisketch constructor

5cc7d20 header: Delete default Minisketch constructor (TheCharlatan)

Pull request description:

  I might be missing a reason for having the default constructor, but it is not used anywhere and trying to use one of its methods will cause a segfault.

ACKs for top commit:
  sipa:
    ACK 5cc7d20

Tree-SHA512: 5d395ce919b0105b644e83cf3d9867c4ee8dd92d3561c56aa72794704f26167465a24d541d6cf266bf49a9fec48ad492edf4ad1083c0ae799335865a23ac462c

Author: sipa

include/minisketch.h

@@ -248,8 +248,8 @@ class Minisketch
     /** Check whether this Minisketch object is valid. */
     explicit operator bool() const noexcept { return bool{m_minisketch}; }
 
-    /** Construct an (invalid) Minisketch object. */
-    Minisketch() noexcept = default;
+    /** Default constructor is deleted. */
+    Minisketch() noexcept = delete;
 
     /** Move constructor. */
     Minisketch(Minisketch&&) noexcept = default;