Minor improvements (some of #1465) (#1493)

* lib/memory.py: use 'if collection' instead of 'if len(collection) > 0'

* commands/__init__.py: use 'not line' instead of 'len(line)==0'

* hexdump.py: use 'not data' instead of 'len(data)==0'

* commands/nearpc.py: use `if p` instead of `if len("%s" % p)>0`

I double checked that this works fine:
```
pwndbg> set nearpc-branch-marker-contiguous
Set contiguous branch marker line for nearpc command to ''.
pwndbg> pi str(pwndbg.commands.nearpc.nearpc_branch_marker_contiguous)
''
pwndbg> pi bool(pwndbg.commands.nearpc.nearpc_branch_marker_contiguous)
False
```

pwndbg/commands/__init__.py

@@ -52,7 +52,7 @@ def list_current_commands():
         line = line.strip()
         # Skip non-command entries
         if (
-            len(line) == 0
+            not line
             or line.startswith("Command class:")
             or line.startswith("Unclassified commands")
         ):

pwndbg/commands/nearpc.py

@@ -191,7 +191,7 @@ def nearpc(pc=None, lines=None, to_string=False, emulate=False):
         # Otherwise if it's a branch and it *is* contiguous, just put
         # and empty line.
         elif prev and any(g in prev.groups for g in (CS_GRP_CALL, CS_GRP_JUMP, CS_GRP_RET)):
-            if len("%s" % nearpc_branch_marker_contiguous) > 0:
+            if nearpc_branch_marker_contiguous:
                 result.append("%s" % nearpc_branch_marker_contiguous)
 
         # For syscall instructions, put the name on the side

pwndbg/hexdump.py

@@ -87,7 +87,7 @@ def hexdump(
             load_color_scheme()
 
         # If there's nothing to print, just print the offset and address and return
-        if len(data) == 0:
+        if not data:
             yield H.offset("+%04x " % len(data)) + H.address("%#08x  " % (address + len(data)))
 
             # Don't allow iterating over this generator again

pwndbg/lib/memory.py

@@ -94,7 +94,7 @@ class Page:
 
     @property
     def is_memory_mapped_file(self) -> bool:
-        return len(self.objfile) > 0 and self.objfile[0] != "[" and self.objfile != "<pt>"
+        return self.objfile and self.objfile[0] != "[" and self.objfile != "<pt>"
 
     @property
     def read(self) -> bool: