OpenAPI: RESTEASY003210 issue with @ApplicationPath("")
I am not a JAX-RS expert, but I think that `@ApplicationPath("")` and `@ApplicationPath("/")` are the same.

Javadoc for `String value();` in `@ApplicationPath`:

> Defines the base URI for all resource URIs. A trailing '/' character will be automatically appended if one is not present.

If this is correct you can continue to read this issue.

---

**Describe the bug**
When using `@ApplicationPath("")` the OpenAPI specification is not served.

**Expected behavior**
```
GET http://localhost:8080/openapi
```

Returns a Yaml OpenAPI.

**Actual behavior**
```
GET http://localhost:8080/openapi
```

Returns:

```
RESTEASY003210: Could not find resource for full path: http://localhost:8080/openapi
```


**To Reproduce**
Steps to reproduce the behavior:
1. Create a simple project with `[cdi, resteasy, resteasy-jsonb, smallrye-openapi, swagger-ui]`
2. Create 2 simple classes:
```java
package com.example.openapi;

import javax.ws.rs.ApplicationPath;
import javax.ws.rs.core.Application;

@ApplicationPath("")
public class RestApplication extends Application {
}
```

```java
package com.example.openapi;

import javax.ws.rs.*;
import javax.ws.rs.core.Response;

import java.io.InputStream;
import java.util.Map;
import java.util.List;
import javax.validation.constraints.*;
import javax.validation.Valid;

@Path("/ping")
public class PingApi {

    @GET
    public Response pingGet() {
        return Response.ok().entity("magic!").build();
    }
}
```
3. Open http://localhost:8080/openapi

**Environment (please complete the following information):**
 - Output of `uname -a` or `ver`: 
```
Darwin MacBook-Pro.local 18.5.0 Darwin Kernel Version 18.5.0: Mon Mar 11 20:40:32 PDT 2019; root:xnu-4903.251.3~3/RELEASE_X86_64 x86_64
```
 - Output of `java -version`: 
```
java version "1.8.0_161"
Java(TM) SE Runtime Environment (build 1.8.0_161-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.161-b12, mixed mode)
```
 - GraalVM version (if different from Java): not used
 - Quarkus version or git rev: 0.17.0

diff --git a/extensions/resteasy/deployment/src/main/java/io/quarkus/resteasy/deployment/ResteasyProcessor.java b/extensions/resteasy/deployment/src/main/java/io/quarkus/resteasy/deployment/ResteasyProcessor.java
index 3c02dd1bbb6..009ab2761f2 100755
--- a/extensions/resteasy/deployment/src/main/java/io/quarkus/resteasy/deployment/ResteasyProcessor.java
+++ b/extensions/resteasy/deployment/src/main/java/io/quarkus/resteasy/deployment/ResteasyProcessor.java
@@ -59,7 +59,7 @@ public void build(
             String path = resteasyServerConfig.get().getPath();
 
             //if JAX-RS is installed at the root location we use a filter, otherwise we use a Servlet and take over the whole mapped path
-            if (resteasyServerConfig.get().getPath().equals("/")) {
+            if (path.equals("/") || path.isEmpty()) {
                 filter.produce(FilterBuildItem.builder(JAX_RS_FILTER_NAME, ResteasyFilter.class.getName()).setLoadOnStartup(1)
                         .addFilterServletNameMapping("default", DispatcherType.REQUEST).setAsyncSupported(true)
                         .build());
['extensions/resteasy/deployment/src/main/java/io/quarkus/resteasy/deployment/ResteasyProcessor.java']