8261547: Minor memory leak reported for Metal Rendering pipeline

Reviewed-by: kcr, aghaisas

Author: prsadhuk

src/java.desktop/macosx/native/libawt_lwawt/java2d/metal/MTLGraphicsConfig.m

@@ -117,14 +117,16 @@
     JNI_COCOA_ENTER(env);
     NSMutableArray * retArray = [NSMutableArray arrayWithCapacity:3];
     [retArray addObject: [NSNumber numberWithInt: (int)displayID]];
-    [retArray addObject: [NSString stringWithUTF8String: JNU_GetStringPlatformChars(env, shadersLibName, 0)]];
+    char *str = JNU_GetStringPlatformChars(env, shadersLibName, 0);
+    [retArray addObject: [NSString stringWithUTF8String: str]];
 
     [ThreadUtilities performOnMainThreadWaiting:YES block:^() {
         [MTLGraphicsConfigUtil _tryLoadMetalLibrary: retArray];
     }];
 
     NSNumber * num = (NSNumber *)[retArray objectAtIndex: 0];
     ret = (jboolean)[num boolValue];
+    JNU_ReleaseStringPlatformChars(env, shadersLibName, str);
     JNI_COCOA_EXIT(env);
     return ret;
 }
@@ -148,14 +150,16 @@
     JNI_COCOA_ENTER(env);
     NSMutableArray * retArray = [NSMutableArray arrayWithCapacity:3];
     [retArray addObject: [NSNumber numberWithInt: (int)displayID]];
-    [retArray addObject: [NSString stringWithUTF8String: JNU_GetStringPlatformChars(env, mtlShadersLib, 0)]];
+    char *str = JNU_GetStringPlatformChars(env, mtlShadersLib, 0);
+    [retArray addObject: [NSString stringWithUTF8String: str]];
 
     [ThreadUtilities performOnMainThreadWaiting:YES block:^() {
         [MTLGraphicsConfigUtil _getMTLConfigInfo: retArray];
     }];
 
     NSNumber * num = (NSNumber *)[retArray objectAtIndex: 0];
     ret = (jlong)[num longValue];
+    JNU_ReleaseStringPlatformChars(env, mtlShadersLib, str);
     JNI_COCOA_EXIT(env);
     return ret;
 }