Fix QDB crash on allocation boundaries

Author: elicn

qiling/debugger/qdb/context.py

@@ -57,7 +57,7 @@ def disasm(self, address: int, detail: bool = False) -> InsnLike:
         """Helper function for disassembling.
         """
 
-        insn_bytes = self.read_insn(address)
+        insn_bytes = self.read_insn(address) or b''
         insn = None
 
         if insn_bytes:
@@ -75,7 +75,7 @@ def disasm_lite(self, address: int) -> Tuple[int, int, str, str]:
             A tuple of: instruction address, size, mnemonic and operands
         """
 
-        insn_bytes = self.read_insn(address)
+        insn_bytes = self.read_insn(address) or b''
         insn = None
 
         if insn_bytes: