title: corrplot causing weird error
body: <p>I have two set matrix defined below:</p>
  
  <p>They contain p values from t-tests between two variables (I know this is bad statistical practice)</p>
  
  <p>I'm trying to use a correlation plot from the <code>corrplot</code> package to plot them</p>
  
  <p>however, when I use the following line:</p>
  
  <pre><code>corrplot(weird, insig = "p-value", p.mat = weird, type = "lower", sig.level = 1-0.95, method = "circle", is.corr = FALSE,  cl.lim=c(0,1), tl.offset=0.4)
  </code></pre>
  
  <p>The normal matrix displays correctly, yet the weird one doesn't. 
  This has caused me many hours of frustration, and I have narrowed the problem down to the <code>insig="p-value"</code> argument, as the corrplot function works as intended without it.</p>
  
  <pre><code>weird&lt;-structure(c(2.22044604925031e-16, 0.018443376602325, 2.12390642555483e-12, 
  2.22044604925031e-16, 0.018443376602325, 2.22044604925031e-16, 
  2.22044604925031e-16, 2.22044604925031e-16, 2.12390642555483e-12, 
  2.22044604925031e-16, 3.00501193636783e-06, 2.5333487645982e-12, 
  2.22044604925031e-16, 2.22044604925031e-16, 2.5333487645982e-12, 
  0.0197044105270931), .Dim = c(4L, 4L), .Dimnames = list(NULL, 
      NULL))
  
  normal&lt;-structure(c(0.34190041513821, 0.957047560166067, 0.680056137259229, 
  0.00101879090792332, 1.2138613135621e-09, 0.406147270030259, 
  0.957047560166067, 0.343145355714736, 0.157301364839312, 0.0223978064844035, 
  2.92279774741867e-07, 0.904700589348579, 0.680056137259229, 0.157301364839312, 
  0.620933486276745, 0.000609313754058382, 2.10803751235147e-10, 
  0.411208816692722, 0.00101879090792332, 0.0223978064844035, 0.000609313754058382, 
  8.78613655419196e-05, 9.15187128142626e-12, 0.197743409064612, 
  1.2138613135621e-09, 2.92279774741867e-07, 2.10803751235147e-10, 
  9.15187128142626e-12, 0.00179242617730144, 0.0159636230788393, 
  0.406147270030259, 0.904700589348579, 0.411208816692722, 0.197743409064612, 
  0.0159636230788393, 1.5372324857583e-07), .Dim = c(6L, 6L), .Dimnames = list(
      NULL, NULL))
  </code></pre>
  
  <p>The weird one
  <img src="https://i.stack.imgur.com/rD1L0.png" alt="The weird result"></p>
  
  <p>The normal one
  <img src="https://i.stack.imgur.com/grPNa.png" alt="The normal result"></p>