Fix time-add/time-sub validity checking

* src/timefns.c (time_arith): Check the first arg for
validity even if the second arg is not finite.
* test/src/timefns-tests.el (time-arith-tests): Test this.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/timefns.c b/src/timefns.c
index 3948f873354..2d545a4f905 100644
--- a/src/timefns.c
+++ b/src/timefns.c
@@ -1035,12 +1035,12 @@ time_arith (Lisp_Object a, Lisp_Object b, bool subtract)
       double db = XFLOAT_DATA (Ffloat_time (b));
       return make_float (subtract ? da - db : da + db);
     }
-  if (FLOATP (b) && !isfinite (XFLOAT_DATA (b)))
-    return subtract ? make_float (-XFLOAT_DATA (b)) : b;
-
   enum timeform aform, bform;
   struct lisp_time ta = lisp_time_struct (a, &aform);
 
+  if (FLOATP (b) && !isfinite (XFLOAT_DATA (b)))
+    return subtract ? make_float (-XFLOAT_DATA (b)) : b;
+
   /* Subtract nil from nil correctly, and handle other eq values
      quicker while we're at it.  Compare here rather than earlier, to
      handle NaNs and check formats.  */