filterPeaks: minNumber must not be higher than the maximal number of MassPeaks objects

[sgibb]

minNumber should be reduced to the maximal number of MassPeaks objects in the current label otherwise all peaks will removed:

library("MALDIquant")

p <- c(createMassPeaks(1:3, 1:3),
       createMassPeaks(1:2, 1:2),
       createMassPeaks(1, 1))

filterPeaks(p, minNumber=2, labels=c(1, 2, 2))

# [[1]]
# S4 class type            : MassPeaks
# Number of m/z values     : 0        
# Range of m/z values      : NA       
# Range of intensity values: NA       
# Range of snr values      : NA       
# Memory usage             : 1.234 KiB
# 
# [[2]]
# S4 class type            : MassPeaks
# Number of m/z values     : 1        
# Range of m/z values      : 1 - 1    
# Range of intensity values: 1 - 1    
# Range of snr values      : NA - NA  
# Memory usage             : 1.258 KiB
# 
# [[3]]
# S4 class type            : MassPeaks    
# Number of m/z values     : 1            
# Range of m/z values      : 1 - 1        
# Range of intensity values: 1e+00 - 1e+00
# Range of snr values      : NA - NA      
# Memory usage             : 1.258 KiB 

expected output:

# warning: reduce minNumber for label "1" because minNumber > n doesn't make sense!

# [[1]]
# S4 class type            : MassPeaks
# Number of m/z values     : 3        
# Range of m/z values      : 1 - 3    
# Range of intensity values: 1 - 3    
# Range of snr values      : NA - NA  
# Memory usage             : 1.281 KiB

[sgibb]

Introduced in #21.

[sgibb]

Since MALDIquant 1.8.16 minFrequency and minNumber could be vectors so this
is not needed any more and we could use minFrequency > 1 and minNumber > n as feature to
remove all peaks (or avoid the generation of a whitelist if mergeWhitelists=TRUE (MALDIquant 1.8.17))