Making the error json into an exception.

src/http.ts

@@ -1268,6 +1268,8 @@ export class LemmyHttp {
         headers: this.headers,
       });
 
+      await this.checkandThrowError(response);
+
       return await response.json();
     } else {
       const response = await fetch(this.buildFullUrl(endpoint), {
@@ -1279,9 +1281,19 @@ export class LemmyHttp {
         body: JSON.stringify(form),
       });
 
+      await this.checkandThrowError(response);
+
       return await response.json();
     }
   }
+
+  private async checkandThrowError(response: Response) {
+    if (!response.ok) {
+      let errJson = await response.json();
+      let errString: string = errJson["error"] ?? response.statusText;
+      throw new Error(errString);
+    }
+  }
 }
 
 function encodeGetParams<BodyType extends object>(p: BodyType): string {