(#5643) Boost.python requires numpy. Fix function _run_python_script().

* Boost.python requires numpy. Fix function _run_python_script(), was broken when script returns empty output.

* Boost: implement PR #5643 feedback from @SSE4. Remove numpy check, needs more investigation

recipes/boost/all/conanfile.py

@@ -528,10 +528,11 @@ def _run_python_script(self, script):
         except ConanException:
             self.output.info("(failed)")
             return None
-        output = output.getvalue().strip()
+        output = output.getvalue()
         # Conan is broken when run_to_output = True
         if "\n-----------------\n" in output:
             output = output.split("\n-----------------\n", 1)[1]
+        output = output.strip()
         return output if output != "None" else None
 
     def _get_python_path(self, name):