bmap: scripts: Fixed missing geometry race condition

The gbmap's weight is defined by the block count stored in the geometry
config field, which should always be present in valid littlefs3 images.

But our scripts routinely try to parse _invalid_ littlefs3 images when
running in parallel with benchmarks/tests (littlefs3 does _not_ support
multiple read/writers), so this was causing exceptions to be thrown.

The fix is to just assume weight=0 when the geometry field is missing.
The image isn't valid, and the gbmap is optional anyways.

scripts/dbgbmap.py

@@ -2778,7 +2778,8 @@ class Gstate:
             block, trunk, cksum, d_ = frombranch(self.data, d); d += d_
             self.btree = Btree.fetchck(
                     mtree.bd, block, trunk,
-                    config.geometry.block_count,
+                    config.geometry.block_count
+                        if config.geometry is not None else 0,
                     cksum)
 
         def repr(self):

scripts/dbgbmapsvg.py

@@ -2808,7 +2808,8 @@ class Gstate:
             block, trunk, cksum, d_ = frombranch(self.data, d); d += d_
             self.btree = Btree.fetchck(
                     mtree.bd, block, trunk,
-                    config.geometry.block_count,
+                    config.geometry.block_count
+                        if config.geometry is not None else 0,
                     cksum)
 
         def repr(self):

scripts/dbglfs3.py

@@ -2735,7 +2735,8 @@ class Gstate:
             block, trunk, cksum, d_ = frombranch(self.data, d); d += d_
             self.btree = Btree.fetchck(
                     mtree.bd, block, trunk,
-                    config.geometry.block_count,
+                    config.geometry.block_count
+                        if config.geometry is not None else 0,
                     cksum)
 
         def repr(self):