[core] put back REF_COUNT_INVALID to be -1, fix finish

Previous commit broke cairo_surface_finish, since it was checking for
ref_count == CAIRO_REF_COUNT_INVALID and bailing.  But, that condition
was reached from destroy, so finish was bailing out early.

src/cairo-font.c

@@ -178,6 +178,9 @@ cairo_font_face_get_type (cairo_font_face_t *font_face)
 unsigned int
 cairo_font_face_get_reference_count (cairo_font_face_t *font_face)
 {
+    if (font_face->ref_count == CAIRO_REF_COUNT_INVALID)
+	return 0;
+
     return font_face->ref_count;
 }
 

src/cairo-pattern.c

@@ -592,6 +592,9 @@ slim_hidden_def (cairo_pattern_destroy);
 unsigned int
 cairo_pattern_get_reference_count (cairo_pattern_t *pattern)
 {
+    if (pattern->ref_count == CAIRO_REF_COUNT_INVALID)
+	return 0;
+
     return pattern->ref_count;
 }
 

src/cairo-scaled-font.c

@@ -638,6 +638,9 @@ slim_hidden_def (cairo_scaled_font_destroy);
 unsigned int
 cairo_scaled_font_get_reference_count (cairo_scaled_font_t *scaled_font)
 {
+    if (scaled_font->ref_count == CAIRO_REF_COUNT_INVALID)
+	return 0;
+
     return scaled_font->ref_count;
 }
 

src/cairo-surface.c

@@ -405,6 +405,9 @@ slim_hidden_def(cairo_surface_destroy);
 unsigned int
 cairo_surface_get_reference_count (cairo_surface_t *surface)
 {
+    if (surface->ref_count == CAIRO_REF_COUNT_INVALID)
+	return 0;
+
     return surface->ref_count;
 }
 

src/cairo.c

@@ -345,6 +345,9 @@ cairo_set_user_data (cairo_t			 *cr,
 unsigned int
 cairo_get_reference_count (cairo_t *cr)
 {
+    if (cr->ref_count == CAIRO_REF_COUNT_INVALID)
+	return 0;
+
     return cr->ref_count;
 }
 

src/cairoint.h

@@ -241,7 +241,7 @@ do {					\
     assert (NOT_REACHED);		\
 } while (0)
 
-#define CAIRO_REF_COUNT_INVALID (0)
+#define CAIRO_REF_COUNT_INVALID ((unsigned int) -1)
 
 #include "cairo-wideint-private.h"