fix: Move BBOX_NONE out of get_bound as only tags have no content

Also ensure that only tags have no content by checking if there
is actually any text being shown by `TJ`

playa/page.py

@@ -1691,10 +1691,27 @@ def bbox(self) -> Rect:
         return get_bound(points)
 
 
+BBOX_NONE = (-1, -1, -1, -1)
+
+
 @dataclass
 class TagObject(ContentObject):
     """A marked content point with no content."""
 
+    @property
+    def bbox(self) -> Rect:
+        """A tag has no content and thus no bounding box.
+
+        To avoid needlessly complicating user code this returns
+        `BBOX_NONE` instead of `None` or throwing a exception.
+        Because that is a specific object, you can reliably check for
+        it with:
+
+            if obj.bbox is BBOX_NONE:
+                ...
+        """
+        return BBOX_NONE
+
 
 @dataclass
 class ImageObject(ContentObject):
@@ -2209,11 +2226,13 @@ def do_BT(self) -> None:
 
     def do_ET(self) -> Iterator[ContentObject]:
         """End a text object"""
-        # Only output text if... there is text to output (we rewrite all text operators to TJ)
+        # Only output text if... there is text to output (we rewrite
+        # all text operators to TJ)
         has_text = False
         for item in self.textobj:
             if item.operator == "TJ":
-                has_text = True
+                if any(b for b in item.args if isinstance(b, bytes)):
+                    has_text = True
         if has_text:
             yield self.create(TextObject, textstate=self.textstate, items=self.textobj)
         else:

playa/utils.py

@@ -253,15 +253,15 @@ def isnumber(x: object) -> bool:
 
 
 _T = TypeVar("_T")
-BBOX_NONE = (-1, -1, -1, -1)
 
 
 def get_bound(pts: Iterable[Point]) -> Rect:
-    """Compute a minimal rectangle that covers all the points."""
-    try:
-        xs, ys = list(zip(*pts))
-    except ValueError:  # Means pts was empty
-        return BBOX_NONE
+    """Compute a minimal rectangle that covers all the points.
+
+    Raises:
+      ValueError on empty input (as there is no bounding box).
+    """
+    xs, ys = list(zip(*pts))
     x0 = min(xs)
     y0 = min(ys)
     x1 = max(xs)