fix: Initialize VIPS_INIT only once

Mihon was crashing somethimes crashing when decoding the first image. I
notice Mihon was decoding two images at the same time, which made me
think it could be a threading issue. Reading libvips documentation, it
states that it is safe, but VIPS_INIT must only be called in a
single-thread. I was calling VIPS_INIT for every decoder created, which
I believe was the issue.

This commit moves VIPS_INIT to JNI_OnLoad, which is called only once
when the library is loaded.

Author: Rodrigodd

library/src/main/cpp/image-decoder/decoder_vips.cpp

@@ -26,12 +26,6 @@ VipsDecoder* try_vips_decoder(std::shared_ptr<Stream>& stream, bool cropBorders,
 VipsDecoder::VipsDecoder(std::shared_ptr<Stream>&& stream, bool cropBorders,
                          cmsHPROFILE targetProfile)
     : stream(std::move(stream)), targetProfile(targetProfile) {
-
-  if (VIPS_INIT("VipsDecoder")) {
-    LOGE("Failed to initialize libvips.");
-    throw std::runtime_error("libvips initialization failed");
-  }
-
   // the VImage does not take ownership of the `stream`.
   this->image = VImage::new_from_buffer(
       this->stream->bytes, this->stream->size, nullptr,

library/src/main/cpp/image-decoder/java_wrapper.cpp

@@ -21,6 +21,12 @@ jint JNI_OnLoad(JavaVM* vm, void*) {
   } else {
     return JNI_ERR;
   }
+
+  if (VIPS_INIT("VipsDecoder")) {
+    LOGE("Failed to initialize libvips.");
+    return JNI_ERR;
+  }
+
   return JNI_VERSION_1_6;
 }