Move type check in collect_exts_file_info to top of loop

The loop body is so large, that the allowed/checked types are very hard
to find.

Author: Flamefire

easybuild/framework/easyblock.py

@@ -553,7 +553,12 @@ def collect_exts_file_info(self, fetch_files=True, verify_checksums=True):
         force_download = build_option('force_download') in [FORCE_DOWNLOAD_ALL, FORCE_DOWNLOAD_SOURCES]
 
         for ext in exts_list:
-            if isinstance(ext, (list, tuple)) and ext:
+            if isinstance(ext, str):
+                exts_sources.append({'name': ext})
+            else:
+                if not isinstance(ext, (list, tuple)) or not ext:
+                    raise EasyBuildError("Extension specified in unknown format (not a string/list/tuple)")
+
                 # expected format: (name, version, options (dict))
                 # name and version can use templates, resolved via parent EC
 
@@ -725,12 +730,6 @@ def collect_exts_file_info(self, fetch_files=True, verify_checksums=True):
 
                     exts_sources.append(ext_src)
 
-            elif isinstance(ext, str):
-                exts_sources.append({'name': ext})
-
-            else:
-                raise EasyBuildError("Extension specified in unknown format (not a string/list/tuple)")
-
         return exts_sources
 
     def obtain_file(self, filename, extension=False, urls=None, download_filename=None, force_download=False,