better error messages when reading timeseries

tests/COLVAR_unparseable_1.xvg

@@ -0,0 +1,11 @@
+84.840004  -2.878293
+84.860004  -2.827750
+84.880004  -2.962375
+84.900004  
+84.920004  -2.748589
+84.940004  -2.726197
+84.960004  -2.802982
+84.980004  -2.771980
+85.000004  -2.706482
+85.020004  -2.776983
+85.040004  -2.883180

tests/COLVAR_unparseable_2.xvg

@@ -0,0 +1,11 @@
+84.840004  -2.878293
+84.860004  -2.827750
+84.880004  -2.962375
+84.900004   qwee
+84.920004  -2.748589
+84.940004  -2.726197
+84.960004  -2.802982
+84.980004  -2.771980
+85.000004  -2.706482
+85.020004  -2.776983
+85.040004  -2.883180

tests/integration.rs

@@ -77,6 +77,36 @@ mod integration {
         ));
     }
 
+    #[test]
+    fn unparseable_timeseries() {
+        let output = Command::new("./target/debug/wham")
+            .args(&["--bins", "100", "--min", "-3.0", "--max", "3.0", "-T", "300"])
+            .args(&["-f", "tests/metadata_unparseable3.dat"])
+            .args(&["-o", "/dev/null"])
+            .output()
+            .expect("failed to execute process");
+        let output = String::from_utf8_lossy(&output.stderr);
+        println!("{}", output);
+        assert!(output.to_string().contains(
+            "Failed to parse line"
+        ));
+    }
+
+    #[test]
+    fn unparseable_timeseries_empty() {
+        let output = Command::new("./target/debug/wham")
+            .args(&["--bins", "100", "--min", "-3.0", "--max", "3.0", "-T", "300"])
+            .args(&["-f", "tests/metadata_unparseable4.dat"])
+            .args(&["-o", "/dev/null"])
+            .output()
+            .expect("failed to execute process");
+        let output = String::from_utf8_lossy(&output.stderr);
+        println!("{}", output);
+        assert!(output.to_string().contains(
+            "Wrong number of columns in line"
+        ));
+    }
+
     #[test]
     fn wham_1d() {;
         Command::new("./target/debug/wham")

tests/metadata_unparseable3.dat

@@ -0,0 +1 @@
+COLVAR_unparseable_2.xvg     -3.0       100

tests/metadata_unparseable4.dat

@@ -0,0 +1 @@
+COLVAR_unparseable_1.xvg     -3.0       100