Bug fix for error handling of the heap commands (#1543)

Fix the bug by adding the missing attribute `symbol` to `SymbolUnresolvableError`, and add the test for it to avoid it happening again

pwndbg/heap/ptmalloc.py

@@ -1252,6 +1252,7 @@ class DebugSymsHeap(GlibcMemoryAllocator):
 class SymbolUnresolvableError(Exception):
     def __init__(self, symbol) -> None:
         super().__init__(f"`{symbol}` can not be resolved via heuristic")
+        self.symbol = symbol
 
 
 class HeuristicHeap(GlibcMemoryAllocator):

tests/gdb-tests/tests/heap/test_heap.py

@@ -429,9 +429,9 @@ def test_heuristic_fail_gracefully(start_binary, is_multi_threaded):
                 "The heuristic for pwndbg.heap.current.%s should fail with SymbolUnresolvableError"
                 % name
             )
-        except SymbolUnresolvableError:
+        except SymbolUnresolvableError as e:
             # That's the only exception we expect
-            pass
+            assert e.symbol  # we should show what symbol we failed to resolve
 
     # Mock all address and mess up the memory
     with mock_for_heuristic(mock_all=True, mess_up_memory=True):