conan: allow repeated executions of `conan build`

conanfile.py

@@ -81,6 +81,7 @@ class Re3Conan(ConanFile):
     def build(self):
         if self.source_folder == self.build_folder:
             raise Exception("cannot build with source_folder == build_folder")
+        try:
             os.unlink(os.path.join(self.install_folder, "Findlibrw.cmake"))
             tools.save("FindOpenAL.cmake",
                        textwrap.dedent(
@@ -113,6 +114,8 @@ class Re3Conan(ConanFile):
                            add_subdirectory("{}" re3)
                            """).format(self.install_folder.replace("\\", "/"),
                                        self.source_folder.replace("\\", "/")))
+        except FileNotFoundError:
+            pass
         cmake = CMake(self)
         cmake.definitions["RE3_AUDIO"] = self._re3_audio
         cmake.definitions["RE3_WITH_OPUS"] = self.options.with_opus