Avoid reading uninitialized end.p for point writes/reads

For point writes and point reads (end.len == 0), end.p is not part of
the API contract and callers may leave it uninitialized -- both the C
and C++ API smoke tests and the fuzz test driver do so.  However,
insertPointWritesOrSorted and check::Job::init unconditionally built a
TrivialSpan from end.p, reading the uninitialized pointer even though
it is never used for point operations.

Move the end span construction into the range-write/range-read branches
so end.p is only read when end.len > 0.  This is semantically identical
but removes the uninitialized reads that MemorySanitizer reports.

ConflictSet.cpp

@@ -3864,11 +3864,10 @@ PRESERVE_NONE void right_side_iter(Job *job, Context *context) {
 void Job::init(const ConflictSet::ReadRange *read, ConflictSet::Result *result,
                Node *root, int64_t oldestVersionFullPrecision) {
   auto begin = TrivialSpan(read->begin.p, read->begin.len);
-  auto end = TrivialSpan(read->end.p, read->end.len);
   if (read->readVersion < oldestVersionFullPrecision) [[unlikely]] {
     *result = ConflictSet::TooOld;
     continuation = complete;
-  } else if (end.size() == 0) {
+  } else if (read->end.len == 0) {
     this->begin = begin;
     this->n = root;
     this->readVersion = InternalVersionT(read->readVersion);
@@ -3876,7 +3875,7 @@ void Job::init(const ConflictSet::ReadRange *read, ConflictSet::Result *result,
     continuation = check::point_read_state_machine::begin;
   } else {
     this->begin = begin;
-    this->end = end;
+    this->end = TrivialSpan(read->end.p, read->end.len);
     this->n = root;
     this->readVersion = InternalVersionT(read->readVersion);
     this->result = result;
@@ -5046,8 +5045,8 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
       for (int i = 0; i < count; ++i) {
         const auto &w = writes[i];
         auto begin = TrivialSpan(w.begin.p, w.begin.len);
-        auto end = TrivialSpan(w.end.p, w.end.len);
         if (w.end.len > 0) {
+          auto end = TrivialSpan(w.end.p, w.end.len);
           addWriteRange(rootParent->children[0], begin, end,
                         InternalVersionT(writeVersion), &writeContext);
         } else {