Account for negative metric values in telemetry (#532)

app/src/main/java/com/geeksville/mesh/NodeInfo.kt

@@ -158,7 +158,7 @@ data class NodeInfo(
     val batteryStr get() = if (batteryLevel in 1..100) String.format("%d%%", batteryLevel) else ""
 
     private fun envFormat(f: String, unit: String, env: Float?): String =
-        if (env != null && env > 0f) String.format(f + unit, env) else ""
+        if (env != null && env != 0f) String.format(f + unit, env) else ""
 
     val envMetricStr
         get() = envFormat("%.1f", "°C ", environmentMetrics?.temperature) +
@@ -211,4 +211,4 @@ data class NodeInfo(
             else -> "%.1f km".format(dist / 1000.0)
         }
     }
-}
+}