Fix memory leak in compression level with non-Integer

This PR fixes a memory leak when an invalid level option is passed to Zstd.compress.

If non-Integer object was given as compression level,
NUM2INT cause a TypeError exception and memory leak.

This changes will release the context if necessary and raise an exception
if non-Integer object was given as compression level.

Author: Watson1978

ext/zstdruby/common.h

@@ -10,11 +10,17 @@
 
 extern VALUE rb_cCDict, rb_cDDict;
 
-static int convert_compression_level(VALUE compression_level_value)
+static int convert_compression_level(ZSTD_CCtx* ctx, VALUE compression_level_value)
 {
   if (NIL_P(compression_level_value)) {
     return ZSTD_CLEVEL_DEFAULT;
   }
+  if (!RB_INTEGER_TYPE_P(compression_level_value)) {
+      if (ctx) {
+          ZSTD_freeCCtx(ctx);
+      }
+      rb_raise(rb_eTypeError, "compression level must be an Integer");
+  }
   return NUM2INT(compression_level_value);
 }
 
@@ -28,7 +34,7 @@ static void set_compress_params(ZSTD_CCtx* const ctx, VALUE kwargs)
 
   int compression_level = ZSTD_CLEVEL_DEFAULT;
   if (kwargs_values[0] != Qundef && kwargs_values[0] != Qnil) {
-    compression_level = convert_compression_level(kwargs_values[0]);
+    compression_level = convert_compression_level(ctx, kwargs_values[0]);
   }
   ZSTD_CCtx_setParameter(ctx, ZSTD_c_compressionLevel, compression_level);
 

ext/zstdruby/zstdruby.c

@@ -169,7 +169,7 @@ static VALUE rb_cdict_initialize(int argc, VALUE *argv, VALUE self)
   VALUE dict;
   VALUE compression_level_value;
   rb_scan_args(argc, argv, "11", &dict, &compression_level_value);
-  int compression_level = convert_compression_level(compression_level_value);
+  int compression_level = convert_compression_level(NULL, compression_level_value);
 
   StringValue(dict);
   char* dict_buffer = RSTRING_PTR(dict);