Changes file for scan-build fixes (#8793)

changes/bug8793

+  o Minor bugfixes:
+    - Fix numerous warnings from the clang "scan-build" static analyzer.
+      Some of these are programming style issues; some of them are false
+      positives that indicated awkward code; some are undefined behavior
+      cases related to constructing (but not using) invalid pointers;
+      some are assumptions about API behavior; some are using
+      sizeof(ptr) when sizeof(*ptr) would be correct; and one or two are
+      genuine bugs that weren't reachable from the rest of the
+      program. Fixes bug 8793; bugfixes on many, many tor versions.