input/Plugin: migrate open() from class Error to C++ exceptions

src/TagFile.cxx

@@ -30,6 +30,8 @@
 #include "input/LocalOpen.hxx"
 #include "thread/Cond.hxx"
 
+#include <stdexcept>
+
 #include <assert.h>
 
 class TagFileScan {
@@ -60,11 +62,12 @@ public:
 
 		/* open the InputStream (if not already open) */
 		if (is == nullptr) {
-			is = OpenLocalInputStream(path_fs,
-						  mutex, cond,
-						  IgnoreError());
-			if (is == nullptr)
+			try {
+				is = OpenLocalInputStream(path_fs,
+							  mutex, cond);
+			} catch (const std::runtime_error &) {
 				return false;
+			}
 		} else
 			is->LockRewind(IgnoreError());