Be more consistent about checking for errors from close()

decode.cpp

@@ -102,7 +102,10 @@ void decode(char *fname, int z, unsigned x, unsigned y) {
 		} else {
 			perror("fstat");
 		}
-		close(fd);
+		if (close(fd) != 0) {
+			perror("close");
+			exit(EXIT_FAILURE);
+		}
 	} else {
 		perror(fname);
 	}

main.cpp

@@ -2167,7 +2167,14 @@ int main(int argc, char **argv) {
 	}
 
 	files_open_at_start = open("/dev/null", O_RDONLY);
-	close(files_open_at_start);
+	if (files_open_at_start < 0) {
+		perror("open /dev/null");
+		exit(EXIT_FAILURE);
+	}
+	if (close(files_open_at_start) != 0) {
+		perror("close");
+		exit(EXIT_FAILURE);
+	}
 
 	if (full_detail <= 0) {
 		full_detail = 12;

tile-join.cpp

@@ -617,7 +617,10 @@ void readcsv(char *fn, std::vector<std::string> &header, std::map<std::string, s
 		}
 	}
 
-	fclose(f);
+	if (fclose(f) != 0) {
+		perror("fclose");
+		exit(EXIT_FAILURE);
+	}
 }
 
 int main(int argc, char **argv) {