Fix void return on BMX280 sensor (#489)

README.md

@@ -4,8 +4,8 @@ ESPurna ("spark" in Catalan) is a custom firmware for ESP8266 based smart switch
 It uses the Arduino Core for ESP8266 framework and a number of 3rd party libraries.
 
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code/espurna/sensors/BMX280Sensor.h

@@ -341,7 +341,7 @@ class BMX280Sensor : public I2CSensor {
                 var1 = ((var1 * var1 * (int64_t)_bmx280_calib.dig_P3)>>8) +
                     ((var1 * (int64_t)_bmx280_calib.dig_P2)<<12);
                 var1 = (((((int64_t)1)<<47)+var1))*((int64_t)_bmx280_calib.dig_P1)>>33;
-                if (var1 == 0) return;  // avoid exception caused by division by zero
+                if (var1 == 0) return SENSOR_ERROR_I2C;  // avoid exception caused by division by zero
 
                 p = 1048576 - adc_P;
                 p = (((p<<31) - var2)*3125) / var1;