Fix #638 - update fiber status in certain cases.

This fixes a regression from changes to janet_try. In some cases, we
would not update the status of a fiber when signaling, which left the
fiber's status as whatever it had previously. This could lead to strange
control flow issues.

test/suite0010.janet

@@ -146,4 +146,18 @@
 # os/execute with environment variables
 (assert (= 0 (os/execute [(dyn :executable) "-e" "(+ 1 2 3)"] :pe {"HELLO" "WORLD"})) "os/execute with env")
 
+# Regression #638
+(assert
+  (= [true :caught]
+     (protect
+       (try
+         (do
+           (ev/sleep 0)
+           (with-dyns []
+             (ev/sleep 0)
+             (error "oops")))
+         ([err] :caught))))
+  "regression #638")
+
+
 (end-suite)