sns: more lenient eneTotal parser

code/espurna/sensor.cpp

@@ -428,14 +428,34 @@ void _sensorRtcmemSaveEnergy(unsigned char index, const sensor::Energy& source)
 
 sensor::Energy _sensorParseEnergy(const String& value) {
     sensor::Energy result;
+    if (!value.length()) {
+        return result;
+    }
+
+    const char* p { value.c_str() };
+
+    char* endp { nullptr };
+    auto kwh = strtoul(p, &endp, 10);
+    if (!endp || (endp == p)) {
+        return result;
+    }
+    result.kwh = kwh;
 
-    const bool separator = value.indexOf('+') > 0;
-    if (value.length() && (separator > 0)) {
-        const String before = value.substring(0, separator);
-        const String after = value.substring(separator + 1);
-        result.kwh = strtoul(before.c_str(), nullptr, 10);
-        result.ws = strtoul(after.c_str(), nullptr, 10);
+    const char* plus { strchr(p, '+') };
+    if (!plus) {
+        return;
+    }
+
+    p = plus + 1;
+    if (*p == '\0') {
+        return result;
+    }
+
+    auto ws = strtoul(p, &endp, 10);
+    if (!endp || (endp == p)) {
+        return result;
     }
+    result.ws = ws;
 
     return result;
 }