Only attempt to stop observation if previously observed (#145)

Author: twyatt

core/src/androidMain/kotlin/Observers.kt

@@ -76,7 +76,7 @@ internal class Observers(
             }
         }
         .onCompletion {
-            if (observations.remove(characteristic, onSubscription) < 1) {
+            if (observations.remove(characteristic, onSubscription) == 0) {
                 try {
                     peripheral.stopObservation(characteristic)
                 } catch (e: NotReadyException) {
@@ -135,7 +135,7 @@ private class Observations {
     ): Int = lock.withLock {
         val actions = observations[characteristic]
         when {
-            actions == null -> 0
+            actions == null -> -1 // No previous observation existed for characteristic.
             actions.count() == 1 -> {
                 observations -= characteristic
                 0

core/src/appleMain/kotlin/Observers.kt

@@ -78,7 +78,7 @@ internal class Observers(
                 }
             }
             .onCompletion {
-                if (observations.remove(characteristic, onSubscription) < 1) {
+                if (observations.remove(characteristic, onSubscription) == 0) {
                     try {
                         peripheral.stopNotifications(characteristic)
                     } catch (e: NotReadyException) {
@@ -139,7 +139,7 @@ private class Observations : IsolateState<MutableMap<Characteristic, MutableList
     ): Int = access {
         val actions = it[characteristic]
         when {
-            actions == null -> 0
+            actions == null -> -1 // No previous observation existed for characteristic.
             actions.count() == 1 -> {
                 it -= characteristic
                 0

core/src/jsMain/kotlin/Observers.kt

@@ -53,7 +53,7 @@ internal class Observers(
             }
         }
         .onCompletion {
-            if (observations.remove(characteristic, onSubscription) < 1) {
+            if (observations.remove(characteristic, onSubscription) == 0) {
                 peripheral.stopObservation(characteristic)
             }
         }
@@ -98,7 +98,7 @@ private class Observations {
     ): Int {
         val actions = observations[characteristic]
         return when {
-            actions == null -> 0
+            actions == null -> -1 // No previous observation existed for characteristic.
             actions.count() == 1 -> {
                 observations -= characteristic
                 0