Fix in TL1_cutom_src_pattern_build test (#6103)

- nvtx is required to generate stubs for dynamic mode. Stubs are
  generated when DALI is installed what happens in
  TL1_cutom_src_pattern_build test
- adds defensive check for dynamic.readers before accessing it to
  prevent AttributeError when dynamic module doesn't have readers attribute

Signed-off-by: Janusz Lisiecki <jlisiecki@nvidia.com>

---------

Signed-off-by: Janusz Lisiecki <jlisiecki@nvidia.com>

Author: JanuszL

dali/python/nvidia/dali/ops/_signatures.py

@@ -760,7 +760,10 @@ def _try_extend_reader_signature(schema: _b.OpSchema, op_name: str):
 
     from nvidia.dali.experimental import dynamic
 
-    op = getattr(dynamic.readers, op_name, None)
+    readers = getattr(dynamic, "readers", None)
+    if readers is None:
+        return ""
+    op = getattr(readers, op_name, None)
     if op is None or not issubclass(op, dynamic.ops.Reader):
         return ""
 

qa/TL1_custom_src_pattern_build/test.sh

@@ -1,6 +1,6 @@
 #!/bin/bash -e
 
-pip_packages='astunparse gast dm-tree black'
+pip_packages='astunparse gast dm-tree black nvtx makefun'
 
 build_and_check() {
   make -j