Fix TypeScript error by adding type guard for 'min' and 'max' properties

The TypeScript compiler was throwing errors because it couldn't find the properties 'min' and 'max' on the type 'BarReading'. The issue arises because TypeScript is unaware that 'min' and 'max' are only accessed when 'readings' is an array of 'LineReadings'. This commit adds a type guard to explicitly inform TypeScript about the type of 'reading', resolving the issue.

src/client/app/utils/exportData.ts

@@ -39,9 +39,11 @@ function convertToCSV(readings: LineReading[] | BarReading[], meter: string, uni
 		csvOutput += `${value},${startTimeStamp},${endTimeStamp}`;
 		// Include min and max in export if appropriate."
 		if (showMinMax) {
-			const min = reading.min * scaling;
-			const max = reading.max * scaling;
-			csvOutput += `,${min},${max}`
+			if ("min" in reading && "max" in reading) {
+				const min = reading.min * scaling;
+				const max = reading.max * scaling;
+				csvOutput += `,${min},${max}`
+			}
 		}
 		csvOutput += '\n';
 	});