MulitQC broke on mirtop data

[gpalidwor]

Description of bug

This bug is the same as the following opened on nf-core/smrna by apeltzer:
nf-core/smrnaseq#137 "Bug in multiqc / mirTop broke"

Diagnosed cause is that mirTop output "ref_miRNA_sum" is not present for all samples which breaks multiQC.

Multiqc error log copied from original bug submission above.

File that triggers the error

No response

MultiQC Error log

/// MultiQC <U+1F50D> | v1.12

|           multiqc | Search path : /work/38/b3bd004777869168b75aaf74ee8d69
|         searching | ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 418/418
|    custom_content | software_versions: Found 1 sample (html)
|    custom_content | nf-core-smrnaseq-summary: Found 1 sample (html)
╭───────────────── Oops! The 'mirtop' MultiQC module broke... ─────────────────╮
│ Please copy this log and report it at                                        │
│ https://github.com/ewels/MultiQC/issues                                      │
│ Please attach a file that triggers the error. The last file found was:       │
│ ./full_mirtop_stats.log                                                      │
│                                                                              │
│ Traceback (most recent call last):                                           │
│   File "/usr/local/lib/python3.10/site-packages/multiqc/multiqc.py", line 65 │
│     output = mod()                                                           │
│   File "/usr/local/lib/python3.10/site-packages/multiqc/modules/mirtop/mirto │
│     self.parse_mirtop_report(f)                                              │
│   File "/usr/local/lib/python3.10/site-packages/multiqc/modules/mirtop/mirto │
│     parsed_data["read_count"] = parsed_data["isomiR_sum"] + parsed_data["ref │
│ KeyError: 'ref_miRNA_sum'                                                    │
│                                                                              │
╰──────────────────────────────────────────────────────────────────────────────╯
|          samtools | Found 158 stats reports
|            fastqc | Found 79 reports
|           multiqc | Compressing plot data
|           multiqc | Report      : multiqc_report.html
|           multiqc | Data        : multiqc_data
|           multiqc | Plots       : multiqc_plots
|           multiqc | MultiQC complete
|           multiqc | 1 flat-image plot used in the report due to large sample numbers
|           multiqc | To force interactive plots, use the '--interactive' flag.
See the documentation.

[ewels]

Test data that may replicate the error: MultiQC/test-data#227