Fix `RefCnt.toString` to not crash after `_ptr` has been assigned null (#1142)

skiko/src/commonMain/kotlin/org/jetbrains/skia/impl/RefCnt.kt

@@ -13,4 +13,18 @@ expect abstract class RefCnt : Managed {
     val refCount: Int
 }
 
+internal fun RefCnt.refCntToString(managedString: String, nullPointer: NativePointer) = buildString {
+    append(managedString)
+    setLength(length - 1)  // remove trailing ')'
+
+    if (_ptr == nullPointer) {
+        append(", disposed")
+    } else {
+        append(", refCount=")
+        append(refCount)
+    }
+
+    append(')')
+}
+
 internal expect fun RefCnt_nGetFinalizer(): NativePointer

skiko/src/jvmMain/kotlin/org/jetbrains/skia/impl/RefCnt.jvm.kt

@@ -14,10 +14,7 @@ actual abstract class RefCnt : Managed {
             Reference.reachabilityFence(this)
         }
 
-    override fun toString(): String {
-        val s = super.toString()
-        return s.substring(0, s.length - 1) + ", refCount=" + refCount + ")"
-    }
+    override fun toString() = refCntToString(super.toString(), 0L)
 
     private object _FinalizerHolder {
         val PTR = _nGetFinalizer()

skiko/src/nativeMain/kotlin/org/jetbrains/skia/impl/RefCnt.native.kt

@@ -14,10 +14,7 @@ actual abstract class RefCnt : Managed {
             reachabilityBarrier(this)
         }
 
-    override fun toString(): String {
-        val s = super.toString()
-        return s.substring(0, s.length - 1) + ", refCount=" + refCount + ")"
-    }
+    override fun toString() = refCntToString(super.toString(), NullPointer)
 
     private object _FinalizerHolder {
         val PTR = RefCnt_nGetFinalizer()

skiko/src/webMain/kotlin/org/jetbrains/skia/impl/RefCnt.js.kt

@@ -12,10 +12,7 @@ actual abstract class RefCnt : Managed {
             return _nGetRefCount(_ptr)
         }
 
-    override fun toString(): String {
-        val s = super.toString()
-        return s.substring(0, s.length - 1) + ", refCount=" + refCount + ")"
-    }
+    override fun toString() = refCntToString(super.toString(), 0)
 }
 
 private object _FinalizerHolder {