raw: tweak seek implementation

libraw uses fseek when doing files, which allows seeking past the end
without problems, so do the same, otherwise when we report oss-fuzz
issues they say "give me an example to reproduce" and since our seek
and their seek don't behave the same it's hard to convince them
to fix their code

src/imageformats/raw.cpp

@@ -141,7 +141,7 @@ public:
         if (whence == SEEK_END) {
             pos = size + o;
         }
-        if (pos < 0 || pos > size || m_device->isSequential()) {
+        if (pos < 0 || m_device->isSequential()) {
             return -1;
         }
         return m_device->seek(pos) ? 0 : -1;