ordered_float:NotNan may contain NaN after unwinding in assignment operators

After using an assignment operators such as `NotNan::add_assign`,
`NotNan::mul_assign`, etc., it was possible for the resulting `NotNan`
value to contain a `NaN`.  This could cause undefined behavior in safe
code, because the safe `NotNan::cmp` method contains internal unsafe
code that assumes the value is never `NaN`.  (It could also cause
undefined behavior in third-party unsafe code that makes the same
assumption, as well as logic errors in safe code.)

This was mitigated starting in version 0.4.0, by panicking if the
assigned value is NaN.  However, in affected versions from 0.4.0 onward,
code that continued after using unwinding to catch this panic could
still observe the invalid value and trigger undefined behavior.

The flaw is fully corrected in versions 1.1.1 and 2.0.1, by ensuring
that the assignment operators panic without modifying the operand, if
the result would be `NaN`.

Fix details:

reem/rust-ordered-float#20
reem/rust-ordered-float#71

Author: mbrubeck

crates/ordered-float/RUSTSEC-0000-0000.md

@@ -0,0 +1,23 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "ordered-float"
+date = "2020-12-06"
+url = "https://github.com/reem/rust-ordered-float/pull/71"
+categories = []
+keywords = ["unwind"]
+
+[versions]
+patched = ["^1.1.1", ">= 2.0.1"]
+unaffected = ["< 0.2.2"]
+
+[affected]
+```
+
+# ordered_float:NotNan may contain NaN after unwinding in assignment operators
+
+After using an assignment operators such as `NotNan::add_assign`, `NotNan::mul_assign`, etc., it was possible for the resulting `NotNan` value to contain a `NaN`.  This could cause undefined behavior in safe code, because the safe `NotNan::cmp` method contains internal unsafe code that assumes the value is never `NaN`.  (It could also cause undefined behavior in third-party unsafe code that makes the same assumption, as well as logic errors in safe code.)
+
+This was mitigated starting in version 0.4.0, by panicking if the assigned value is NaN.  However, in affected versions from 0.4.0 onward, code that continued after using unwinding to catch this panic could still observe the invalid value and trigger undefined behavior.
+
+The flaw is fully corrected in versions 1.1.1 and 2.0.1, by ensuring that the assignment operators panic without modifying the operand, if the result would be `NaN`.