m[vector] Recover vector from error in .reset()

src/hb-vector.hh

@@ -80,7 +80,12 @@ struct hb_vector_t
     fini ();
   }
 
-  void reset () { resize (0); }
+  void reset ()
+  {
+    if (unlikely (in_error ()))
+      allocated = length; // Big hack!
+    resize (0);
+  }
 
   hb_vector_t& operator = (const hb_vector_t &o)
   {
@@ -181,7 +186,7 @@ struct hb_vector_t
   /* Allocate for size but don't adjust length. */
   bool alloc (unsigned int size)
   {
-    if (unlikely (allocated < 0))
+    if (unlikely (in_error ()))
       return false;
 
     if (likely (size <= (unsigned) allocated))
@@ -195,7 +200,7 @@ struct hb_vector_t
 
     Type *new_array = nullptr;
     bool overflows =
-      (int) new_allocated < 0 ||
+      (int) in_error () ||
       (new_allocated < (unsigned) allocated) ||
       hb_unsigned_mul_overflows (new_allocated, sizeof (Type));
     if (likely (!overflows))