[gexiv2] Minor compiler warnings fixes

[Jens Georg <jensgeorg src gnome org>]

commit 1aa6f39714f1165c05ac527a40103751d2c97fbb
Author: Jens Georg <mail jensge org>
Date:   Sun Nov 15 23:10:08 2020 +0100

    Minor compiler warnings fixes

 gexiv2/gexiv2-metadata.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/gexiv2/gexiv2-metadata.cpp b/gexiv2/gexiv2-metadata.cpp
index 5a2a2bb..ab27b0f 100644
--- a/gexiv2/gexiv2-metadata.cpp
+++ b/gexiv2/gexiv2-metadata.cpp
@@ -131,7 +131,7 @@ public:
         return this->read (&b, 1) == 1 ? b : EOF;
     }
 
-    void transfer(Exiv2::BasicIo& src) override {
+    void transfer(Exiv2::BasicIo& /*src*/) override {
         // Does not seem necessary for Read-only support
     }
 
@@ -184,12 +184,12 @@ public:
         }
     }
 
-    Exiv2::byte* mmap(bool writable) override { return NULL; }
+    Exiv2::byte* mmap(bool /*writable*/) override { return nullptr; }
 
     int munmap() override { return 0; }
 
     long tell() const override {
-        if (_seekable != NULL && g_seekable_can_seek (_seekable)) {
+        if (_seekable != nullptr && g_seekable_can_seek (_seekable)) {
             return static_cast<long>(g_seekable_tell (_seekable));
         } else {
             return -1;