Fix cda6f24f: don't ignore binary-dir if it happens to be working-dir (#11431)

Some of our code ignores the SP_WORKING_DIR for some actions, which
means that if, for example, your SP_BINARY_DIR is the same as your
SP_WORKING_DIR, neither is scanned.

Instead, only add SP_WORKING_DIR if it is unique.

(cherry picked from commit c059ce0c97)

src/fileio.cpp

@@ -88,6 +88,8 @@ static void FillValidSearchPaths(bool only_local_path)
 
 	btree::btree_set<std::string_view> seen{};
 	for (Searchpath sp = SP_FIRST_DIR; sp < NUM_SEARCHPATHS; sp++) {
+		if (sp == SP_WORKING_DIR) continue;
+
 		if (only_local_path) {
 			switch (sp) {
 				case SP_WORKING_DIR:      // Can be influence by "-c" option.
@@ -106,6 +108,13 @@ static void FillValidSearchPaths(bool only_local_path)
 			_valid_searchpaths.emplace_back(sp);
 		}
 	}
+
+	/* The working-directory is special, as it is controlled by _do_scan_working_directory.
+	 * Only add the search path if it isn't already in the set. To preserve the same order
+	 * as the enum, insert it in the front. */
+	if (IsValidSearchPath(SP_WORKING_DIR) && seen.count(_searchpaths[SP_WORKING_DIR]) == 0) {
+		_valid_searchpaths.insert(_valid_searchpaths.begin(), SP_WORKING_DIR);
+	}
 }
 
 /**